The type implementing this traversable
The type implementing this traversable
A lazier implementation of WithFilter than TraversableLike's.
A class supporting filtered operations.
A class supporting filtered operations. Instances of this class are
returned by method withFilter
.
Is the tail of this stream defined?
Is the tail of this stream defined?
Create a new stream which contains all elements of this stream followed by
all elements of Traversable that
.
Create a new stream which contains all elements of this stream followed by
all elements of Traversable that
.
The element type of the returned collection.That
the class of the returned collection. Where possible, That
is
the same class as the current collection class Repr
, but this
depends on the element type B
being admissible for that class,
which means that an implicit instance of type CanBuildFrom[Repr, B, That]
is found.
The scala.collection.GenTraversableOnce the be contatenated
to this Stream
.
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type B
.
A new collection containing the result of concatenating this
with
that
.
This method doesn't cause the Stream
to be fully realized but it
should be noted that using the ++
operator from another collection type
could cause infinite realization of a Stream
. For example, referring to
the definition of fibs
in the preamble, the following would never return:
List(BigInt(12)) ++ fibs
.
It's subtle why this works. We know that if the target type of the
scala.collection.mutable.Builder That
is either a Stream
, or one of
its supertypes, or undefined, then StreamBuilder
will be chosen for the
implicit. We recognize that fact and optimize to get more laziness.
As with ++
, returns a new collection containing the elements from the
left operand followed by the elements from the right operand.
As with ++
, returns a new collection containing the elements from the
left operand followed by the elements from the right operand.
It differs from ++
in that the right operand determines the type of
the resulting collection rather than the left one.
Mnemonic: the COLon is on the side of the new COLlection type.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = LinkedList(2) y: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val z = x ++: y z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
This overload exists because: for the implementation of ++:
we should
reuse that of ++
because many collections override it with more
efficient versions.
Since TraversableOnce
has no ++
method, we have to implement that
directly, but Traversable
and down can use the overload.
the element type of the returned collection.
the class of the returned collection. Where possible, That
is
the same class as the current collection class Repr
, but this
depends on the element type B
being admissible for that class,
which means that an implicit instance of type CanBuildFrom[Repr, B, That]
is found.
the traversable to append.
an implicit value of class CanBuildFrom
which determines
the result class That
from the current representation type Repr
and
and the new element type B
.
a new collection of type That
which contains all elements
of this traversable collection followed by all elements of that
.
[use case] As with ++
, returns a new collection containing the elements from the left operand followed by the
elements from the right operand.
As with ++
, returns a new collection containing the elements from the left operand followed by the
elements from the right operand.
It differs from ++
in that the right operand determines the type of
the resulting collection rather than the left one.
Mnemonic: the COLon is on the side of the new COLlection type.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = LinkedList(2) y: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val z = x ++: y z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
the element type of the returned collection.
the traversable to append.
a new stream which contains all elements of this stream
followed by all elements of that
.
[use case] A copy of the stream with an element prepended.
A copy of the stream with an element prepended.
Note that :-ending operators are right associative (see example).
A mnemonic for +:
vs. :+
is: the COLon goes on the COLlection side.
Also, the original stream is not modified, so you will want to capture the result.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = 2 +: x y: List[Int] = List(2, 1) scala> println(x) List(1)
the prepended element
a new stream consisting of elem
followed
by all elements of this stream.
Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.
Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.
Note: /:
is alternate syntax for foldLeft
; z /: xs
is the same as
xs foldLeft z
.
Examples:
Note that the folding function used to compute b is equivalent to that used to compute c.
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = (5 /: a)(_+_) b: Int = 15 scala> val c = (5 /: a)((x,y) => x + y) c: Int = 15
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this traversable or iterator,
going left to right with the start value z
on the left:
op(...op(op(z, x_1), x_2), ..., x_n)
where x_{1}, ..., x_{n}
are the elements of this traversable or iterator.
[use case] A copy of this stream with an element appended.
A copy of this stream with an element appended.
A mnemonic for +:
vs. :+
is: the COLon goes on the COLlection side.
Note: will not terminate for infinite-sized collections.
Example:
scala> val a = List(1) a: List[Int] = List(1) scala> val b = a :+ 2 b: List[Int] = List(1, 2) scala> println(a) List(1)
the appended element
a new stream consisting of
all elements of this stream followed by elem
.
Applies a binary operator to all elements of this traversable or iterator and a start value, going right to left.
Applies a binary operator to all elements of this traversable or iterator and a start value, going right to left.
Note: :\
is alternate syntax for foldRight
; xs :\ z
is the same as
xs foldRight z
.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
Examples:
Note that the folding function used to compute b is equivalent to that used to compute c.
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = (a :\ 5)(_+_) b: Int = 15 scala> val c = (a :\ 5)((x,y) => x + y) c: Int = 15
the result type of the binary operator.
the start value
the binary operator
the result of inserting op
between consecutive elements of this traversable or iterator,
going right to left with the start value z
on the right:
op(x_1, op(x_2, ... op(x_n, z)...))
where x_{1}, ..., x_{n}
are the elements of this traversable or iterator.
Write all defined elements of this iterable into given string builder.
Write all defined elements of this iterable into given string builder.
The written text begins with the string start
and is finished by the string
end
. Inside, the string representations of defined elements (w.r.t.
the method toString()
) are separated by the string sep
. The method will
not force evaluation of undefined elements. A tail of such elements will be
represented by a "?"
instead.
The collection.mutable.StringBuilder factory to which we need to add the string elements.
The prefix of the resulting string (e.g. "Stream(")
The separator between elements of the resulting string (e.g. ",")
The end of the resulting string (e.g. ")")
The original collection.mutable.StringBuilder containing the resulting string.
Appends all elements of this traversable or iterator to a string builder.
Appends all elements of this traversable or iterator to a string builder.
The written text consists of the string representations (w.r.t. the method
toString
) of all elements of this traversable or iterator without any separator string.
Example:
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> val h = a.addString(b) h: StringBuilder = 1234
the string builder to which elements are appended.
the string builder b
to which elements were appended.
Appends all elements of this traversable or iterator to a string builder using a separator string.
Appends all elements of this traversable or iterator to a string builder using a separator string.
The written text consists of the string representations (w.r.t. the method toString
)
of all elements of this traversable or iterator, separated by the string sep
.
Example:
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = new StringBuilder() b: StringBuilder = scala> a.addString(b, ", ") res0: StringBuilder = 1, 2, 3, 4
the string builder to which elements are appended.
the separator string.
the string builder b
to which elements were appended.
Aggregates the results of applying an operator to subsequent elements.
Aggregates the results of applying an operator to subsequent elements.
This is a more general form of fold
and reduce
. It has similar
semantics, but does not require the result to be a supertype of the
element type. It traverses the elements in different partitions
sequentially, using seqop
to update the result, and then applies
combop
to results from different partitions. The implementation of
this operation may operate on an arbitrary number of collection
partitions, so combop
may be invoked an arbitrary number of times.
For example, one might want to process some elements and then produce
a Set
. In this case, seqop
would process an element and append it
to the list, while combop
would concatenate two lists from different
partitions together. The initial value z
would be an empty set.
pc.aggregate(Set[Int]())(_ += process(_), _ ++ _)
Another example is calculating geometric mean from a collection of doubles (one would typically require big doubles for this).
the type of accumulated results
the initial value for the accumulated result of the partition - this
will typically be the neutral element for the seqop
operator (e.g.
Nil
for list concatenation or 0
for summation) and may be evaluated
more than once
an operator used to accumulate results within a partition
an associative operator used to combine results from different partitions
Composes this partial function with a transformation function that gets applied to results of this partial function.
Composes this partial function with a transformation function that gets applied to results of this partial function.
the result type of the transformation function.
the transformation function
a partial function with the same domain as this partial function, which maps
arguments x
to k(this(x))
.
The stream resulting from the concatenation of this stream with the argument stream.
The stream resulting from the concatenation of this stream with the argument stream.
The stream that gets appended to this stream
The stream containing elements of this stream and the traversable object.
Selects an element by its index in the sequence.
Selects an element by its index in the sequence.
Note: the execution of apply
may take time proportial to the index value.
the element of this sequence at index idx
, where 0
indicates the first element.
if idx
does not satisfy 0 <= idx < length
.
Applies this partial function to the given argument when it is contained in the function domain.
Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.
Note that expression pf.applyOrElse(x, default)
is equivalent to
if(pf isDefinedAt x) pf(x) else default(x)
except that applyOrElse
method can be implemented more efficiently.
For all partial function literals the compiler generates an applyOrElse
implementation which
avoids double evaluation of pattern matchers and guards.
This makes applyOrElse
the basis for the efficient implementation for many operations and scenarios, such as:
orElse
/andThen
chains does not lead to
excessive apply
/isDefinedAt
evaluationlift
and unlift
do not evaluate source functions twice on each invocationrunWith
allows efficient imperative-style combining of partial functions
with conditionally applied actions For non-literal partial function classes with nontrivial isDefinedAt
method
it is recommended to override applyOrElse
with custom implementation that avoids
double isDefinedAt
evaluation. This may result in better performance
and more predictable behavior w.r.t. side effects.
the function argument
the fallback function
the result of this function or fallback function application.
2.10
Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.
Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.
The object with which this iterable collection should be compared
true
, if this iterable collection can possibly equal that
, false
otherwise. The test
takes into consideration only the run-time types of objects but ignores their elements.
[use case] Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.
Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.
the element type of the returned collection.
the partial function which filters and maps the stream.
a new stream resulting from applying the given partial function
pf
to each element on which it is defined and collecting the results.
The order of the elements is preserved.
Finds the first element of the traversable or iterator for which the given partial function is defined, and applies the partial function to it.
Finds the first element of the traversable or iterator for which the given partial function is defined, and applies the partial function to it.
Note: may not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the partial function
an option value containing pf applied to the first
value for which it is defined, or None
if none exists.
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
Iterates over combinations.
Iterates over combinations.
An Iterator which traverses the possible n-element combinations of this sequence.
"abbbc".combinations(2) = Iterator(ab, ac, bb, bc)
The factory companion object that builds instances of class Stream
.
The factory companion object that builds instances of class Stream
.
(or its Iterable
superclass where class Stream
is not a Seq
.)
Composes two instances of Function1 in a new Function1, with this function applied last.
Composes two instances of Function1 in a new Function1, with this function applied last.
the type to which function g
can be applied
a function A => T1
a new function f
such that f(x) == apply(g(x))
Tests whether this sequence contains a given value as an element.
Tests whether this sequence contains a given value as an element.
Note: may not terminate for infinite-sized collections.
the element to test.
true
if this sequence has an element that is equal (as
determined by ==
) to elem
, false
otherwise.
Tests whether this sequence contains a given sequence as a slice.
Tests whether this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
true
if this sequence contains a slice with the same elements
as that
, otherwise false
.
[use case] Copies elements of this stream to an array.
Copies elements of this stream to an array.
Fills the given array xs
with at most len
elements of
this stream, starting at position start
.
Copying will stop once either the end of the current stream is reached,
or the end of the array is reached, or len
elements have been copied.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
the maximal number of elements to copy.
[use case] Copies values of this stream to an array.
Copies values of this stream to an array.
Fills the given array xs
with values of this stream.
Copying will stop once either the end of the current stream is reached,
or the end of the array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
[use case] Copies values of this stream to an array.
Copies values of this stream to an array.
Fills the given array xs
with values of this stream, beginning at index start
.
Copying will stop once either the end of the current stream is reached,
or the end of the array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
Copies all elements of this traversable or iterator to a buffer.
Copies all elements of this traversable or iterator to a buffer.
Note: will not terminate for infinite-sized collections.
The buffer to which elements are copied.
Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.
Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.
the type of the elements of that
the other sequence
the test predicate, which relates elements from both sequences
true
if both sequences have the same length and
p(x, y)
is true
for all corresponding elements x
of this sequence
and y
of that
, otherwise false
.
Counts the number of elements in the traversable or iterator which satisfy a predicate.
Counts the number of elements in the traversable or iterator which satisfy a predicate.
the predicate used to test elements.
the number of elements satisfying the predicate p
.
[use case] Computes the multiset difference between this stream and another sequence.
Computes the multiset difference between this stream and another sequence.
Note: will not terminate for infinite-sized collections.
the sequence of elements to remove
a new stream which contains all elements of this stream
except some of occurrences of elements that also appear in that
.
If an element value x
appears
n times in that
, then the first n occurrences of x
will not form
part of the result, but any following occurrences will.
Builds a new stream from this stream in which any duplicates (as
determined by ==
) have been removed.
Builds a new stream from this stream in which any duplicates (as
determined by ==
) have been removed. Among duplicate elements, only the
first one is retained in the resulting Stream
.
A new Stream
representing the result of applying distinctness to
the original Stream
.
// Creates a Stream where every element is duplicated def naturalsFrom(i: Int): Stream[Int] = i #:: { i #:: naturalsFrom(i + 1) } naturalsFrom(1) take 6 mkString ", " // produces: "1, 1, 2, 2, 3, 3" (naturalsFrom(1) distinct) take 6 mkString ", " // produces: "1, 2, 3, 4, 5, 6"
Selects all elements except first n ones.
Selects all elements except first n ones.
the number of elements to drop from this stream.
a stream consisting of all elements of this stream except the first n
ones, or else the
empty stream, if this stream has less than n
elements.
Selects all elements except last n ones.
Selects all elements except last n ones.
Note: lazily evaluated; will terminate for infinite-sized collections.
The number of elements to take
a stream consisting of all elements of this stream except the last n
ones, or else the
empty stream, if this stream has less than n
elements.
Returns the a Stream
representing the longest suffix of this iterable
whose first element does not satisfy the predicate p
.
Returns the a Stream
representing the longest suffix of this iterable
whose first element does not satisfy the predicate p
.
the test predicate.
A new Stream
representing the results of applying p
to the
oringal Stream
.
// Assume we have a Stream that takes the first 20 natural numbers def naturalsLt50(i: Int): Stream[Int] = i #:: { if (i < 20) naturalsLt50(i * + 1) else Stream.Empty } naturalsLt50(0) dropWhile { _ < 10 } // produces: "10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20"
This method realizes the entire Stream
beyond the truth value of
the predicate p
.
Tests whether this sequence ends with the given sequence.
Tests whether this sequence ends with the given sequence.
Note: will not terminate for infinite-sized collections.
the sequence to test
true
if this sequence has that
as a suffix, false
otherwise.
The equals method for arbitrary sequences.
The equals method for arbitrary sequences. Compares this sequence to some other object.
The object to compare the sequence to
true
if that
is a sequence that has the same elements as
this sequence in the same order, false
otherwise
Tests whether a predicate holds for some of the elements of this sequence.
Tests whether a predicate holds for some of the elements of this sequence.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
false
if this sequence is empty, otherwise true
if the given predicate p
holds for some of the elements of this sequence, otherwise false
Returns all the elements of this Stream
that satisfy the predicate p
in a new Stream
- i.e.
Returns all the elements of this Stream
that satisfy the predicate p
in a new Stream
- i.e. it is still a lazy data structure. The order of
the elements is preserved
the predicate used to filter the stream.
the elements of this stream satisfying p
.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) naturalsFrom(1) 10 } filter { _ % 5 == 0 } take 10 mkString(", ") // produces
Selects all elements of this traversable collection which do not satisfy a predicate.
Selects all elements of this traversable collection which do not satisfy a predicate.
the predicate used to test elements.
a new traversable collection consisting of all elements of this traversable collection that do not satisfy the given
predicate p
. The order of the elements is preserved.
Finds the first element of the sequence satisfying a predicate, if any.
Finds the first element of the sequence satisfying a predicate, if any.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
an option value containing the first element in the sequence
that satisfies p
, or None
if none exists.
Applies the given function f
to each element of this stream, then
concatenates the results.
Applies the given function f
to each element of this stream, then
concatenates the results. As with map
this function does not need to
realize the entire Stream
but continues to keep it as a lazy Stream
.
The element type of the returned collection That.
the class of the returned collection. Where possible, That
is
the same class as the current collection class Repr
, but this
depends on the element type B
being admissible for that class,
which means that an implicit instance of type CanBuildFrom[Repr, B, That]
is found.
the function to apply on each element.
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type B
.
f(a_{0}) ::: ... ::: f(a_{n})
if
this stream is [a_{0}, ..., a_{n}]
.
// Let's create a Stream of Vectors, each of which contains the // collection of Fibonacci numbers up to the current value. We // can then 'flatMap' that Stream. val fibVec: Stream[Vector[Int]] = Vector(0) #:: Vector(0, 1) #:: fibVec.zip(fibVec.tail).map(n => { n._2 ++ Vector(n._1.last + n._2.last) }) fibVec take 5 foreach println // prints // Vector(0) // Vector(0, 1) // Vector(0, 1, 1) // Vector(0, 1, 1, 2) // Vector(0, 1, 1, 2, 3) // If we now want to `flatMap` across that stream by adding 10 // we can see what the series turns into: fibVec.flatMap(_.map(_ + 10)) take 15 mkString(", ") // produces: 10, 10, 11, 10, 11, 11, 10, 11, 11, 12, 10, 11, 11, 12, 13
Note: Currently flatMap
will evaluate as much of the Stream as needed
until it finds a non-empty element for the head, which is non-lazy.
Evaluates and concatenates all elements within the Stream
into a new
flattened Stream
.
Evaluates and concatenates all elements within the Stream
into a new
flattened Stream
.
The type of the elements of the resulting Stream
.
an implicit conversion which asserts that the element
type of this stream is a GenTraversable
.
A new Stream
of type B
of the flattened elements of this
Stream
.
val sov: Stream[Vector[Int]] = Vector(0) #:: Vector(0, 0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 } sov.flatten take 10 mkString ", " // produces: "0, 0, 0, 0, 0, 0, 0, 0, 0, 0"
Folds the elements of this traversable or iterator using the specified associative binary operator.
Folds the elements of this traversable or iterator using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
a type parameter for the binary operator, a supertype of A
.
a neutral element for the fold operation; may be added to the result
an arbitrary number of times, and must not change the result (e.g., Nil
for list concatenation,
0 for addition, or 1 for multiplication.)
a binary operator that must be associative
the result of applying fold operator op
between all the elements and z
Stream specialization of foldLeft which allows GC to collect along the way.
Stream specialization of foldLeft which allows GC to collect along the way.
The type of value being accumulated.
The initial value seeded into the function op
.
The operation to perform on successive elements of the Stream
.
The accumulated value from successive applications of op
.
Applies a binary operator to all elements of this sequence and a start value, going right to left.
Applies a binary operator to all elements of this sequence and a start value, going right to left.
Note: will not terminate for infinite-sized collections.
the result type of the binary operator.
the start value.
the result of inserting op
between consecutive elements of this sequence,
going right to left with the start value z
on the right:
op(x_1, op(x_2, ... op(x_n, z)...))
where x_{1}, ..., x_{n}
are the elements of this sequence.
Tests whether a predicate holds for all elements of this sequence.
Tests whether a predicate holds for all elements of this sequence.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
true
if this sequence is empty, otherwise true
if the given predicate p
holds for all elements of this sequence, otherwise false
.
Forces evaluation of the whole stream and returns it.
Forces evaluation of the whole stream and returns it.
The fully realized Stream
.
Often we use Stream
s to represent an infinite set or series. If
that's the case for your particular Stream
then this function will never
return and will probably crash the VM with an OutOfMemory
exception.
Apply the given function f
to each element of this linear sequence
(while respecting the order of the elements).
Apply the given function f
to each element of this linear sequence
(while respecting the order of the elements).
The treatment to apply to each element.
This function will force the realization of the entire stream
unless the f
throws an exception.
Overridden here as final to trigger tail-call optimization, which replaces 'this' with 'tail' at each iteration. This is absolutely necessary for allowing the GC to collect the underlying stream as elements are consumed.
Returns string formatted according to given format
string.
Returns string formatted according to given format
string.
Format strings are as for String.format
(@see java.lang.String.format).
The generic builder that builds instances of CC at arbitrary element types.
The generic builder that builds instances of CC at arbitrary element types.
Partitions this traversable collection into a map of traversable collections according to some discriminator function.
Partitions this traversable collection into a map of traversable collections according to some discriminator function.
Note: this method is not re-implemented by views. This means when applied to a view it will always force the view and return a new traversable collection.
the type of keys returned by the discriminator function.
the discriminator function.
A map from keys to traversable collections such that the following invariant holds:
(xs groupBy f)(k) = xs filter (x => f(x) == k)
That is, every key k
is bound to a traversable collection of those elements x
for which f(x)
equals k
.
Partitions elements in fixed size iterable collections.
Partitions elements in fixed size iterable collections.
the number of elements per group
An iterator producing iterable collections of size size
, except the
last will be less than size size
if the elements don't divide evenly.
scala.collection.Iterator, method grouped
Tests whether this stream is known to have a finite size.
Tests whether this stream is known to have a finite size.
All strict collections are known to have finite size. For a non-strict
collection such as Stream
, the predicate returns true
if all
elements have been computed. It returns false
if the stream is
not yet evaluated to the end.
Note: many collection methods will not work on collections of infinite sizes.
true
if this collection is known to have finite size,
false
otherwise.
Hashcodes for Seq
produce a value from the hashcodes of all the
elements of the sequence.
Hashcodes for Seq
produce a value from the hashcodes of all the
elements of the sequence.
Selects the first element of this iterable collection.
Selects the first element of this iterable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this iterable collection.
if the iterable collection is empty.
Optionally selects the first element.
Optionally selects the first element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this traversable collection if it is nonempty,
None
if it is empty.
[use case] Finds index of first occurrence of some value in this stream after or at some start index.
Finds index of first occurrence of some value in this stream after or at some start index.
Note: may not terminate for infinite-sized collections.
the element value to search for.
the start index
the index >= from
of the first element of this stream that is equal (as determined by ==
)
to elem
, or -1
, if none exists.
[use case] Finds index of first occurrence of some value in this stream.
Finds index of first occurrence of some value in this stream.
Note: may not terminate for infinite-sized collections.
the element value to search for.
the index of the first element of this stream that is equal (as determined by ==
)
to elem
, or -1
, if none exists.
Finds first index after or at a start index where this sequence contains a given sequence as a slice.
Finds first index after or at a start index where this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
the start index
the first index >= from
such that the elements of this sequence starting at this index
match the elements of sequence that
, or -1
of no such subsequence exists.
Finds first index where this sequence contains a given sequence as a slice.
Finds first index where this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
the first index such that the elements of this sequence starting at this index
match the elements of sequence that
, or -1
of no such subsequence exists.
Finds index of the first element satisfying some predicate after or at some start index.
Finds index of the first element satisfying some predicate after or at some start index.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the start index
the index >= from
of the first element of this sequence that satisfies the predicate p
,
or -1
, if none exists.
Finds index of first element satisfying some predicate.
Finds index of first element satisfying some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the index of the first element of this general sequence that satisfies the predicate p
,
or -1
, if none exists.
Produces the range of all indices of this sequence.
Produces the range of all indices of this sequence.
a Range
value from 0
to one less than the length of this sequence.
The stream without its last element.
The stream without its last element.
A new Stream
containing everything but the last element. If your
Stream
represents an infinite series, this method will not return.
if the stream is empty.
Iterates over the inits of this traversable collection.
Iterates over the inits of this traversable collection. The first value will be this
traversable collection and the final one will be an empty traversable collection, with the intervening
values the results of successive applications of init
.
an iterator over all the inits of this traversable collection
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
[use case] Computes the multiset intersection between this stream and another sequence.
Computes the multiset intersection between this stream and another sequence.
Note: may not terminate for infinite-sized collections.
the sequence of elements to intersect with.
a new stream which contains all elements of this stream
which also appear in that
.
If an element value x
appears
n times in that
, then the first n occurrences of x
will be retained
in the result, but any following occurrences will be omitted.
Tests whether this sequence contains given index.
Tests whether this sequence contains given index.
The implementations of methods apply
and isDefinedAt
turn a Seq[A]
into
a PartialFunction[Int, A]
.
true
if this sequence contains an element at position idx
, false
otherwise.
Tests whether this sequence is empty.
Tests whether this sequence is empty.
true
if the sequence contain no elements, false
otherwise.
Tests whether this traversable collection can be repeatedly traversed.
Tests whether this traversable collection can be repeatedly traversed.
true
A lazier Iterator than LinearSeqLike's.
A lazier Iterator than LinearSeqLike's.
the new iterator
Selects the last element.
Selects the last element.
The last element of this sequence.
If the sequence is empty.
[use case] Finds index of last occurrence of some value in this stream before or at a given end index.
Finds index of last occurrence of some value in this stream before or at a given end index.
the element value to search for.
the end index.
the index <= end
of the last element of this stream that is equal (as determined by ==
)
to elem
, or -1
, if none exists.
[use case] Finds index of last occurrence of some value in this stream.
Finds index of last occurrence of some value in this stream.
Note: will not terminate for infinite-sized collections.
the element value to search for.
the index of the last element of this stream that is equal (as determined by ==
)
to elem
, or -1
, if none exists.
Finds last index before or at a given end index where this sequence contains a given sequence as a slice.
Finds last index before or at a given end index where this sequence contains a given sequence as a slice.
the sequence to test
the end index
the last index <= end
such that the elements of this sequence starting at this index
match the elements of sequence that
, or -1
of no such subsequence exists.
Finds last index where this sequence contains a given sequence as a slice.
Finds last index where this sequence contains a given sequence as a slice.
Note: will not terminate for infinite-sized collections.
the sequence to test
the last index such that the elements of this sequence starting a this index
match the elements of sequence that
, or -1
of no such subsequence exists.
Finds index of last element satisfying some predicate before or at given end index.
Finds index of last element satisfying some predicate before or at given end index.
the predicate used to test elements.
the index <= end
of the last element of this sequence that satisfies the predicate p
,
or -1
, if none exists.
Finds index of last element satisfying some predicate.
Finds index of last element satisfying some predicate.
Note: will not terminate for infinite-sized collections.
the predicate used to test elements.
the index of the last element of this general sequence that satisfies the predicate p
,
or -1
, if none exists.
Optionally selects the last element.
Optionally selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the last element of this traversable collection$ if it is nonempty,
None
if it is empty.
Returns the length of this Stream
.
Returns the length of this Stream
.
The length of this Stream
.
In order to compute the length of the Stream
, it must first be
fully realized, which could cause the complete evaluation of an infinite
series, assuming that's what your Stream
represents.
Compares the length of this sequence to a test value.
Compares the length of this sequence to a test value.
the test value that gets compared with the length.
A value x
where
x < 0 if this.length < len x == 0 if this.length == len x > 0 if this.length > len
The method as implemented here does not call length
directly; its running time
is O(length min len)
instead of O(length)
. The method should be overwritten
if computing length
is cheap.
Turns this partial function into a plain function returning an Option
result.
Turns this partial function into a plain function returning an Option
result.
a function that takes an argument x
to Some(this(x))
if this
is defined for x
, and to None
otherwise.
Function.unlift
Returns the stream resulting from applying the given function f
to each
element of this stream.
Returns the stream resulting from applying the given function f
to each
element of this stream. This returns a lazy Stream
such that it does not
need to be fully realized.
The element type of the returned collection That.
the class of the returned collection. Where possible, That
is
the same class as the current collection class Repr
, but this
depends on the element type B
being admissible for that class,
which means that an implicit instance of type CanBuildFrom[Repr, B, That]
is found.
function to apply to each element.
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type B
.
f(a_{0}), ..., f(a_{n})
if this sequence is a_{0}, ..., a_{n}
.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) naturalsFrom(1).map(_ + 10) take 5 mkString(", ") // produces: "11, 12, 13, 14, 15"
[use case] Finds the largest element.
Finds the largest element.
the largest element of this stream.
[use case] Finds the first element which yields the largest value measured by function f.
Finds the first element which yields the largest value measured by function f.
The result type of the function f.
The measuring function.
the first element of this stream with the largest value measured by function f.
[use case] Finds the smallest element.
Finds the smallest element.
the smallest element of this stream
[use case] Finds the first element which yields the smallest value measured by function f.
Finds the first element which yields the smallest value measured by function f.
The result type of the function f.
The measuring function.
the first element of this stream with the smallest value measured by function f.
Displays all elements of this stream in a string using start, end, and separator strings.
Displays all elements of this stream in a string using start, end, and separator strings.
the starting string.
the separator string.
the ending string.
a string representation of this stream. The resulting string
begins with the string start
and ends with the string
end
. Inside, the string representations (w.r.t. the method
toString
) of all elements of this stream are separated by
the string sep
.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Displays all elements of this stream in a string.
Displays all elements of this stream in a string.
a string representation of this stream. In the resulting string
the string representations (w.r.t. the method toString
)
of all elements of this stream follow each other without any
separator string.
Displays all elements of this stream in a string using a separator string.
Displays all elements of this stream in a string using a separator string.
the separator string.
a string representation of this stream. In the resulting string
the string representations (w.r.t. the method toString
)
of all elements of this stream are separated by the string sep
.
List(1, 2, 3).mkString("|") = "1|2|3"
The builder that builds instances of type CC[A]
The builder that builds instances of type CC[A]
Tests whether the traversable or iterator is not empty.
Tests whether the traversable or iterator is not empty.
true
if the traversable or iterator contains at least one element, false
otherwise.
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
the argument type of the fallback function
the result type of the fallback function
the fallback function
a partial function which has as domain the union of the domains
of this partial function and that
. The resulting partial function
takes x
to this(x)
where this
is defined, and to that(x)
where it is not.
Returns a new sequence of given length containing the elements of this sequence followed by zero or more occurrences of given elements.
Returns a new sequence of given length containing the elements of this sequence followed by zero or more occurrences of given elements.
The type of the value to pad with.
The type contained within the resulting Stream
.
The number of elements to pad into the Stream
.
The value of the type B
to use for padding.
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type B
.
A new Stream
representing the collection with values padding off
to the end. If your Stream
represents an infinite series, this method will
not return.
def naturalsFrom(i: Int): Stream[Int] = i #:: { if (i < 5) naturalsFrom(i + 1) else Stream.Empty } naturalsFrom(1) padTo(10, 0) foreach println // prints // 1 // 2 // 3 // 4 // 5 // 0 // 0 // 0 // 0 // 0
Returns a parallel implementation of this collection.
Returns a parallel implementation of this collection.
For most collection types, this method creates a new parallel collection by copying
all the elements. For these collection, par
takes linear time. Mutable collections
in this category do not produce a mutable parallel collection that has the same
underlying dataset, so changes in one collection will not be reflected in the other one.
Specific collections (e.g. ParArray
or mutable.ParHashMap
) override this default
behaviour by creating a parallel collection which shares the same underlying dataset.
For these collections, par
takes constant or sublinear time.
All parallel collections return a reference to themselves.
a parallel implementation of this collection
The default par
implementation uses the combiner provided by this method
to create a new parallel collection.
The default par
implementation uses the combiner provided by this method
to create a new parallel collection.
a combiner for the parallel collection of type ParRepr
Returns all the elements of this stream that satisfy the predicate p
returning of scala.Tuple2 of Stream
s obeying the partition predicate
p
.
Returns all the elements of this stream that satisfy the predicate p
returning of scala.Tuple2 of Stream
s obeying the partition predicate
p
. The order of the elements is preserved.
the predicate used to filter the stream.
the elements of this stream satisfying p
.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) val parts = naturalsFrom(1) partition { _ % 2 == 0 } parts._1 take 10 mkString ", " // produces: "2, 4, 6, 8, 10, 12, 14, 16, 18, 20" parts._2 take 10 mkString ", " // produces: "1, 3, 5, 7, 9, 11, 13, 15, 17, 19"
[use case] Produces a new stream where a slice of elements in this stream is replaced by another sequence.
Produces a new stream where a slice of elements in this stream is replaced by another sequence.
the index of the first replaced element
the number of elements to drop in the original stream
a new stream consisting of all elements of this stream
except that replaced
elements starting from from
are replaced
by patch
.
Iterates over distinct permutations.
Iterates over distinct permutations.
An Iterator which traverses the distinct permutations of this sequence.
"abb".permutations = Iterator(abb, bab, bba)
Returns the length of the longest prefix whose elements all satisfy some predicate.
Returns the length of the longest prefix whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the length of the longest prefix of this general sequence
such that every element of the segment satisfies the predicate p
.
Prints elements of this stream one by one, separated by sep
.
Prints elements of this stream one by one, separated by sep
.
The separator string printed between consecutive elements.
Prints elements of this stream one by one, separated by commas.
[use case] Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
the product of all elements in this stream of numbers of type Int
.
Instead of Int
, any other type T
with an implicit Numeric[T]
implementation
can be used as element type of the stream and as result type of product
.
Examples of such types are: Long
, Float
, Double
, BigInt
.
Reduces the elements of this traversable or iterator using the specified associative binary operator.
Reduces the elements of this traversable or iterator using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
A type parameter for the binary operator, a supertype of A
.
A binary operator that must be associative.
The result of applying reduce operator op
between all the elements if the traversable or iterator is nonempty.
if this traversable or iterator is empty.
Stream specialization of reduceLeft which allows GC to collect along the way.
Stream specialization of reduceLeft which allows GC to collect along the way.
The type of value being accumulated.
The operation to perform on successive elements of the Stream
.
The accumulated value from successive applications of f
.
Optionally applies a binary operator to all elements of this traversable or iterator, going left to right.
Optionally applies a binary operator to all elements of this traversable or iterator, going left to right.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceLeft(op)
is this traversable or iterator is nonempty,
None
otherwise.
Reduces the elements of this traversable or iterator, if any, using the specified associative binary operator.
Reduces the elements of this traversable or iterator, if any, using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
A type parameter for the binary operator, a supertype of A
.
A binary operator that must be associative.
An option value containing result of applying reduce operator op
between all
the elements if the collection is nonempty, and None
otherwise.
Applies a binary operator to all elements of this sequence, going right to left.
Applies a binary operator to all elements of this sequence, going right to left.
Note: will not terminate for infinite-sized collections.
the result type of the binary operator.
the binary operator.
the result of inserting op
between consecutive elements of this sequence,
going right to left:
op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
where x_{1}, ..., x_{n}
are the elements of this sequence.
if this sequence is empty.
Optionally applies a binary operator to all elements of this traversable or iterator, going right to left.
Optionally applies a binary operator to all elements of this traversable or iterator, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceRight(op)
is this traversable or iterator is nonempty,
None
otherwise.
The collection of type traversable collection underlying this TraversableLike
object.
The collection of type traversable collection underlying this TraversableLike
object.
By default this is implemented as the TraversableLike
object itself,
but this can be overridden.
A list consisting of all elements of this list in reverse order.
A list consisting of all elements of this list in reverse order.
A new Stream
containing the representing of the original Stream
in reverse order.
def naturalsFrom(i: Int): Stream[Int] = i #:: { if (i < 5) naturalsFrom(i + 1) else Stream.Empty } (naturalsFrom(1) reverse) foreach println // prints // 5 // 4 // 3 // 2 // 1
This function must realize the entire Stream
in order to perform
this operation so if your Stream
represents an infinite sequence then
this function will never return.
An iterator yielding elements in reversed order.
An iterator yielding elements in reversed order.
Note: will not terminate for infinite-sized collections.
Note: xs.reverseIterator
is the same as xs.reverse.iterator
but might be more efficient.
an iterator yielding the elements of this sequence in reversed order
[use case] Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.
Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.
Note: will not terminate for infinite-sized collections.
Note: xs.reverseMap(f)
is the same as xs.reverse.map(f)
but might be more efficient.
the element type of the returned collection.
the function to apply to each element.
a new stream resulting from applying the given function
f
to each element of this stream and collecting the results in reversed order.
Composes this partial function with an action function which gets applied to results of this partial function.
Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.
Note that expression pf.runWith(action)(x)
is equivalent to
if(pf isDefinedAt x) { action(pf(x)); true } else false
except that runWith
is implemented via applyOrElse
and thus potentially more efficient.
Using runWith
avoids double evaluation of pattern matchers and guards for partial function literals.
the action function
a function which maps arguments x
to isDefinedAt(x)
. The resulting function
runs action(this(x))
where this
is defined.
2.10
applyOrElse
.
[use case] Checks if the other iterable collection contains the same elements in the same order as this stream.
Checks if the other iterable collection contains the same elements in the same order as this stream.
Note: will not terminate for infinite-sized collections.
the collection to compare with.
true
, if both collections contain the same elements in the same order, false
otherwise.
Computes a prefix scan of the elements of the collection.
Computes a prefix scan of the elements of the collection.
Note: The neutral element z
may be applied more than once.
element type of the resulting collection
type of the resulting collection
neutral element for the operator op
the associative operator for the scan
combiner factory which provides a combiner
a new traversable collection containing the prefix scan of the elements in this traversable collection
Create a new stream which contains all intermediate results of applying the operator to subsequent elements left to right.
Create a new stream which contains all intermediate results of applying the
operator to subsequent elements left to right. scanLeft
is analogous to
foldLeft
.
the type of the elements in the resulting collection
the actual type of the resulting collection
The initial value for the scan.
A function that will apply operations to successive values in the
Stream
against previous accumulated results.
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type B
.
A new collection containing the modifications from the application
of op
.
This works because the target type of the
scala.collection.mutable.Builder That
is a Stream
.
Produces a collection containing cumulative results of applying the operator going right to left.
Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
Example:
List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
the type of the elements in the resulting collection
the actual type of the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
an implicit value of class CanBuildFrom
which determines
the result class That
from the current representation type Repr
and
and the new element type B
.
collection with intermediate results
(Changed in version 2.9.0) The behavior of scanRight
has changed. The previous behavior can be reproduced with scanRight.reverse.
Computes length of longest segment whose elements all satisfy some predicate.
Computes length of longest segment whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the index where the search starts.
the length of the longest segment of this sequence starting from index from
such that every element of the segment satisfies the predicate p
.
A version of this collection with all of the operations implemented sequentially (i.e.
A version of this collection with all of the operations implemented sequentially (i.e. in a single-threaded manner).
This method returns a reference to this collection. In parallel collections, it is redefined to return a sequential implementation of this collection. In both cases, it has O(1) complexity.
a sequential view of the collection.
The size of this sequence, equivalent to length
.
The size of this sequence, equivalent to length
.
Note: will not terminate for infinite-sized collections.
the number of elements in this sequence.
A substream starting at index from
and extending up to (but not including)
index until
.
A substream starting at index from
and extending up to (but not including)
index until
. This returns a Stream
that is lazily evaluated.
The index of the first element of the returned subsequence
The index of the element following the returned subsequence
A new string containing the elements requested from start
until
end
.
naturalsFrom(0) slice(50, 60) mkString ", " // produces: "50, 51, 52, 53, 54, 55, 56, 57, 58, 59"
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
the number of elements per group
the distance between the first elements of successive groups (defaults to 1)
An iterator producing iterable collections of size size
, except the
last and the only element will be truncated if there are
fewer elements than size.
scala.collection.Iterator, method sliding
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
the number of elements per group
An iterator producing iterable collections of size size
, except the
last and the only element will be truncated if there are
fewer elements than size.
scala.collection.Iterator, method sliding
Sorts this Seq
according to the Ordering which results from transforming
an implicitly given Ordering with a transformation function.
Sorts this Seq
according to the Ordering which results from transforming
an implicitly given Ordering with a transformation function.
the target type of the transformation f
, and the type where
the ordering ord
is defined.
the transformation function mapping elements
to some other domain B
.
the ordering assumed on domain B
.
a sequence consisting of the elements of this sequence
sorted according to the ordering where x < y
if
ord.lt(f(x), f(y))
.
val words = "The quick brown fox jumped over the lazy dog".split(' ') // this works because scala.Ordering will implicitly provide an Ordering[Tuple2[Int, Char]] words.sortBy(x => (x.length, x.head)) res0: Array[String] = Array(The, dog, fox, the, lazy, over, brown, quick, jumped)
Note: will not terminate for infinite-sized collections.
Sorts this sequence according to a comparison function.
Sorts this sequence according to a comparison function.
Note: will not terminate for infinite-sized collections.
The sort is stable. That is, elements that are equal (as determined by
lt
) appear in the same order in the sorted sequence as in the original.
the comparison function which tests whether its first argument precedes its second argument in the desired ordering.
a sequence consisting of the elements of this sequence
sorted according to the comparison function lt
.
List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) = List("Bob", "John", "Steve", "Tom")
Sorts this sequence according to an Ordering.
Sorts this sequence according to an Ordering.
The sort is stable. That is, elements that are equal (as determined by
lt
) appear in the same order in the sorted sequence as in the original.
the ordering to be used to compare elements.
a sequence consisting of the elements of this sequence
sorted according to the ordering ord
.
Splits this sequence into a prefix/suffix pair according to a predicate.
Splits this sequence into a prefix/suffix pair according to a predicate.
Note: c span p
is equivalent to (but possibly more efficient than)
(c takeWhile p, c dropWhile p)
, provided the evaluation of the
predicate p
does not cause any side-effects.
a pair consisting of the longest prefix of this sequence whose
elements all satisfy p
, and the rest of this sequence.
Splits this stream into two at a given position.
Splits this stream into two at a given position.
Note: c splitAt n
is equivalent to (but possibly more efficient than)
(c take n, c drop n)
.
the position at which to split.
a pair of streams consisting of the first n
elements of this stream, and the other elements.
Tests whether this sequence contains the given sequence at a given index.
Tests whether this sequence contains the given sequence at a given index.
Note: If the both the receiver object this
and the argument
that
are infinite sequences this method may not terminate.
the sequence to test
the index where the sequence is searched.
true
if the sequence that
is contained in this sequence at
index offset
, otherwise false
.
Tests whether this general sequence starts with the given sequence.
Tests whether this general sequence starts with the given sequence.
the sequence to test
true
if this collection has that
as a prefix, false
otherwise.
Defines the prefix of this object's toString
representation as Stream
.
Defines the prefix of this object's toString
representation as Stream
.
a string representation which starts the result of toString
applied to this stream. By default the string prefix is the
simple name of the collection class stream.
[use case] Sums up the elements of this collection.
Sums up the elements of this collection.
the sum of all elements in this stream of numbers of type Int
.
Instead of Int
, any other type T
with an implicit Numeric[T]
implementation
can be used as element type of the stream and as result type of sum
.
Examples of such types are: Long
, Float
, Double
, BigInt
.
Selects all elements except the first.
Selects all elements except the first.
Note: might return different results for different runs, unless the underlying collection type is ordered.
a traversable collection consisting of all elements of this traversable collection except the first one.
if the traversable collection is empty.
Iterates over the tails of this traversable collection.
Iterates over the tails of this traversable collection. The first value will be this
traversable collection and the final one will be an empty traversable collection, with the intervening
values the results of successive applications of tail
.
an iterator over all the tails of this traversable collection
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Returns the n
first elements of this Stream
as another Stream
, or
else the whole Stream
, if it has less than n
elements.
Returns the n
first elements of this Stream
as another Stream
, or
else the whole Stream
, if it has less than n
elements.
The result of take
is, again, a Stream
meaning that it also does not
make any needless evaluations of the Stream
itself, delaying that until
the usage of the resulting Stream
.
the number of elements to take.
the n
first elements of this stream.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) scala> naturalsFrom(5) take 5 res1: scala.collection.immutable.Stream[Int] = Stream(5, ?) scala> naturalsFrom(5) take 5 mkString ", " // produces: "5, 6, 7, 8, 9"
Returns the rightmost n
elements from this iterable.
Returns the rightmost n
elements from this iterable.
the number of elements to take
The last n
elements from this Stream
.
Take serious caution here. If the Stream
represents an infinite
series then this function will not return. The right most elements of
an infinite series takes an infinite amount of time to produce.
Returns the longest prefix of this Stream
whose elements satisfy the
predicate p
.
Returns the longest prefix of this Stream
whose elements satisfy the
predicate p
.
the test predicate.
A new Stream
representing the values that satisfy the predicate
p
.
+ naturalsFrom(0) takeWhile { _ < 5 } mkString ", " produces: "0, 1, 2, 3, 4"
The underlying collection seen as an instance of
.Seq
The underlying collection seen as an instance of
.
By default this is implemented as the current collection object itself,
but this can be overridden.
Seq
[use case] Converts this stream into another by copying all elements.
Converts this stream into another by copying all elements.
Note: will not terminate for infinite-sized collections.
The collection type to build.
a new collection containing all elements of this stream.
[use case] Converts this stream to an array.
Converts this stream to an array.
Note: will not terminate for infinite-sized collections.
an array containing all elements of this stream.
An ClassTag
must be available for the element type of this stream.
Uses the contents of this traversable or iterator to create a new mutable buffer.
Uses the contents of this traversable or iterator to create a new mutable buffer.
Note: will not terminate for infinite-sized collections.
a buffer containing all elements of this traversable or iterator.
A conversion from collections of type Repr
to
objects.Seq
A conversion from collections of type Repr
to
objects.
By default this is implemented as just a cast, but this can be overridden.
Seq
Converts this traversable or iterator to an indexed sequence.
Converts this traversable or iterator to an indexed sequence.
Note: will not terminate for infinite-sized collections.
an indexed sequence containing all elements of this traversable or iterator.
Returns this iterable collection as an iterable collection.
Returns this iterable collection as an iterable collection.
A new collection will not be built; lazy collections will stay lazy.
Note: will not terminate for infinite-sized collections.
an Iterable
containing all elements of this iterable collection.
Returns an Iterator over the elements in this iterable collection.
Returns an Iterator over the elements in this iterable collection. Produces the same
result as iterator
.
Note: will not terminate for infinite-sized collections.
an Iterator containing all elements of this iterable collection.
Converts this traversable or iterator to a list.
Converts this traversable or iterator to a list.
Note: will not terminate for infinite-sized collections.
a list containing all elements of this traversable or iterator.
[use case] Converts this stream to a map.
Converts this stream to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.
Note: will not terminate for infinite-sized collections.
a map of type immutable.Map[T, U]
containing all key/value pairs of type (T, U)
of this stream.
Converts this immutable sequence to a sequence.
Converts this immutable sequence to a sequence.
Note: will not terminate for infinite-sized collections.
A new collection will not be built; in particular, lazy sequences will stay lazy.
a sequence containing all elements of this immutable sequence.
Converts this traversable or iterator to a set.
Converts this traversable or iterator to a set.
Note: will not terminate for infinite-sized collections.
a set containing all elements of this traversable or iterator.
Converts this stream to a stream.
Converts this stream to a stream.
a stream containing all elements of this stream.
Converts this stream to a string.
Converts this stream to a string.
a string representation of this collection. By default this
string consists of the stringPrefix
of this stream, followed
by all elements separated by commas and enclosed in parentheses.
Converts this traversable collection to an unspecified Traversable.
Converts this traversable collection to an unspecified Traversable. Will return the same collection if this instance is already Traversable.
Note: will not terminate for infinite-sized collections.
a Traversable containing all elements of this traversable collection.
Converts this traversable or iterator to a Vector.
Converts this traversable or iterator to a Vector.
Note: will not terminate for infinite-sized collections.
a vector containing all elements of this traversable or iterator.
Transposes this collection of traversable collections into a collection of collections.
Transposes this collection of traversable collections into a collection of collections.
The resulting collection's type will be guided by the static type of collection. For example:
val xs = List( Set(1, 2, 3), Set(4, 5, 6)).transpose // xs == List( // List(1, 4), // List(2, 5), // List(3, 6)) val ys = Vector( List(1, 2, 3), List(4, 5, 6)).transpose // ys == Vector( // Vector(1, 4), // Vector(2, 5), // Vector(3, 6))
the type of the elements of each traversable collection.
an implicit conversion which asserts that the
element type of this collection is a Traversable
.
a two-dimensional collection of collections which has as nth row the nth column of this collection.
(Changed in version 2.9.0) transpose
throws an IllegalArgumentException
if collections are not uniformly sized.
if all collections in this collection are not of the same size.
[use case] Produces a new sequence which contains all elements of this stream and also all elements of a given sequence.
Produces a new sequence which contains all elements of this stream and also all elements of
a given sequence. xs union ys
is equivalent to xs ++ ys
.
Another way to express this
is that xs union ys
computes the order-presevring multi-set union of xs
and ys
.
union
is hence a counter-part of diff
and intersect
which also work on multi-sets.
Note: will not terminate for infinite-sized collections.
the sequence to add.
a new stream which contains all elements of this stream
followed by all elements of that
.
Converts this collection of pairs into two collections of the first and second half of each pair.
Converts this collection of pairs into two collections of the first and second half of each pair.
val xs = CC( (1, "one"), (2, "two"), (3, "three")).unzip // xs == (CC(1, 2, 3), // CC(one, two, three))
the type of the first half of the element pairs
the type of the second half of the element pairs
an implicit conversion which asserts that the element type of this collection is a pair.
a pair of collections, containing the first, respectively second half of each element pair of this collection.
Converts this collection of triples into three collections of the first, second, and third element of each triple.
Converts this collection of triples into three collections of the first, second, and third element of each triple.
val xs = CC( (1, "one", '1'), (2, "two", '2'), (3, "three", '3')).unzip3 // xs == (CC(1, 2, 3), // CC(one, two, three), // CC(1, 2, 3))
the type of the first member of the element triples
the type of the second member of the element triples
the type of the third member of the element triples
an implicit conversion which asserts that the element type of this collection is a triple.
a triple of collections, containing the first, second, respectively third member of each element triple of this collection.
[use case] A copy of this stream with one single replaced element.
A copy of this stream with one single replaced element.
the position of the replacement
the replacing element
a copy of this stream with the element at position index
replaced by elem
.
Creates a non-strict view of this stream.
Creates a non-strict view of this stream.
a non-strict view of this stream.
Creates a non-strict view of a slice of this sequence.
Creates a non-strict view of a slice of this sequence.
Note: the difference between view
and slice
is that view
produces
a view of the current sequence, whereas slice
produces a new sequence.
Note: view(from, to)
is equivalent to view.slice(from, to)
the index of the first element of the view
the index of the element following the view
a non-strict view of a slice of this sequence, starting at index from
and extending up to (but not including) index until
.
Creates a non-strict filter of this stream.
Creates a non-strict filter of this stream.
Note: the difference between c filter p
and c withFilter p
is that
the former creates a new collection, whereas the latter only
restricts the domain of subsequent map
, flatMap
, foreach
,
and withFilter
operations.
the predicate used to test elements.
an object of class WithFilter
, which supports
map
, flatMap
, foreach
, and withFilter
operations.
All these operations apply to those elements of this stream
which satisfy the predicate p
.
Returns a stream formed from this stream and the specified stream that
by associating each element of the former with the element at the same
position in the latter.
Returns a stream formed from this stream and the specified stream that
by associating each element of the former with the element at the same
position in the latter.
If one of the two streams is longer than the other, its remaining elements are ignored.
The return type of this function may not be obvious. The lazy aspect of
the returned value is different than that of partition
. In partition
we get back a scala.Tuple2 of two lazy Stream
s whereas here we get
back a single lazy Stream
of scala.Tuple2s where the
scala.Tuple2's type signature is (A1, B)
.
The type of the first parameter of the zipped tuple
The type of the second parameter of the zipped tuple
The type of the returned Stream
.
The iterable providing the second half of each result pair
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type (A1, B)
.
Stream({a_{0},b_{0}}, ...,
{a_{min(m,n)},b_{min(m,n)})}
when
Stream(a_{0}, ..., a_{m})
zip Stream(b_{0}, ..., b_{n})
is invoked.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) naturalsFrom(1) zip naturalsFrom(2) take 5 foreach println // prints // (1,2) // (2,3) // (3,4) // (4,5) // (5,6)
[use case] Returns a stream formed from this stream and another iterable collection by combining corresponding elements in pairs.
Returns a stream formed from this stream and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
the element to be used to fill up the result if this stream is shorter than that
.
the element to be used to fill up the result if that
is shorter than this stream.
a new stream containing pairs consisting of
corresponding elements of this stream and that
. The length
of the returned collection is the maximum of the lengths of this stream and that
.
If this stream is shorter than that
, thisElem
values are used to pad the result.
If that
is shorter than this stream, thatElem
values are used to pad the result.
Zips this iterable with its indices.
Zips this iterable with its indices. s.zipWithIndex
is equivalent to s
zip s.indices
.
This method is much like zip
in that it returns a single lazy Stream
of
scala.Tuple2.
The type of the first element of the scala.Tuple2 in the resulting stream.
The type of the resulting Stream
.
an implicit value of class CanBuildFrom
which determines the
result class That
from the current representation type Repr
and the new element type (A1, Int)
.
Stream({a_{0},0}, ..., {a_{n},n)}
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) (naturalsFrom(1) zipWithIndex) take 5 foreach println // prints // (1,0) // (2,1) // (3,2) // (4,3) // (5,4)
(stream: MonadOps[A]).filter(p)
(stream: MonadOps[A]).flatMap(f)
(stream: MonadOps[A]).map(f)
(stream: MonadOps[A]).withFilter(p)
The class
Stream
implements lazy lists where elements are only evaluated when they are needed. Here is an example:The
Stream
class also employs memoization such that previously computed values are converted fromStream
elements to concrete values of typeA
. To illustrate, we will alter body of thefibs
value above and take some more values:There are a number of subtle points to the above example.
fibs
is aval
not a method. The memoization of theStream
requires us to have somewhere to store the information and aval
allows us to do that.Stream
is actually being modified during access, this does not change the notion of its immutability. Once the values are memoized they do not change and values that have yet to be memoized still "exist", they simply haven't been realized yet.Stream
creates a structure much like scala.collection.immutable.List. So long as something is holding on to the head, the head holds on to the tail, and so it continues recursively. If, on the other hand, there is nothing holding on to the head (e.g. we useddef
to define theStream
) then once it is no longer being used directly, it disappears.Stream
, and a stream holds its own head. For computations of this sort where memoization is not desired, useIterator
when possible.tail
works at all is of interest. In the definition offibs
we have an initial(0, 1, Stream(...))
sotail
is deterministic. If we deinfedfibs
such that only0
were concretely known then the act of determiningtail
would require the evaluation oftail
which would cause an infinite recursion and stack overflow. If we define a definition where the tail is not initially computable then we're going to have an infinite recursion:The definition of
fibs
above creates a larger number of objects than necessary depending on how you might want to implement it. The following implementation provides a more "cost effective" implementation due to the fact that it has a more direct route to the numbers themselves:the type of the elements contained in this stream.
1.1 08/08/03
2.8
"Scala's Collection Library overview" section on
Streams
for more information.