trait Traversable[A] extends collection.Traversable[A] with GenericTraversableTemplate[A, Traversable] with TraversableLike[A, Traversable[A]] with Mutable
A trait for traversable collections that can be mutated.
This is a base trait of all kinds of mutable Scala collections. It
implements the behavior common to all collections, in terms of a method
foreach
with signature:
def foreach[U](f: Elem => U): Unit
Collection classes mixing in this trait provide a concrete
foreach
method which traverses all the
elements contained in the collection, applying a given function to each.
They also need to provide a method newBuilder
which creates a builder for collections of the same kind.
A traversable class might or might not have two properties: strictness and orderedness. Neither is represented as a type.
The instances of a strict collection class have all their elements
computed before they can be used as values. By contrast, instances of
a non-strict collection class may defer computation of some of their
elements until after the instance is available as a value.
A typical example of a non-strict collection class is a
scala.collection.immutable.Stream.
A more general class of examples are TraversableViews
.
If a collection is an instance of an ordered collection class, traversing
its elements with foreach
will always visit elements in the
same order, even for different runs of the program. If the class is not
ordered, foreach
can visit elements in different orders for
different runs (but it will keep the same order in the same run).'
A typical example of a collection class which is not ordered is a
HashMap
of objects. The traversal order for hash maps will
depend on the hash codes of its elements, and these hash codes might
differ from one run to the next. By contrast, a LinkedHashMap
is ordered because its foreach
method visits elements in the
order they were inserted into the HashMap
.
- Source
- Traversable.scala
- Alphabetic
- By Inheritance
- Traversable
- Mutable
- Traversable
- GenTraversable
- GenericTraversableTemplate
- TraversableLike
- GenTraversableLike
- Parallelizable
- TraversableOnce
- GenTraversableOnce
- FilterMonadic
- HasNewBuilder
- AnyRef
- Any
- by CollectionsHaveToParArray
- by MonadOps
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- by alternateImplicit
- Hide All
- Show All
- Public
- All
Type Members
-
class
WithFilter extends FilterMonadic[A, Repr]
A class supporting filtered operations.
A class supporting filtered operations. Instances of this class are returned by method
withFilter
.- Definition Classes
- TraversableLike
-
type
Self = Traversable[A]
The type implementing this traversable
The type implementing this traversable
- Attributes
- protected[this]
- Definition Classes
- TraversableLike
Value Members
-
final
def
!=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
- returns
true
if !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
-
final
def
##(): Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
-
def
+(other: String): String
- Implicit
- This member is added by an implicit conversion from Traversable[A] to any2stringadd[Traversable[A]] performed by method any2stringadd in scala.Predef.
- Definition Classes
- any2stringadd
-
def
++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
Returns a new traversable collection containing the elements from the left hand operand followed by the elements from the right hand operand.
Returns a new traversable collection containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the traversable collection is the most specific superclass encompassing the element types of the two operands.
- B
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 classRepr
, but this depends on the element typeB
being admissible for that class, which means that an implicit instance of typeCanBuildFrom[Repr, B, That]
is found.- that
the traversable to append.
- bf
an implicit value of class
CanBuildFrom
which determines the result classThat
from the current representation typeRepr
and the new element typeB
.- returns
a new collection of type
That
which contains all elements of this traversable collection followed by all elements ofthat
.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
++:[B >: A, That](that: collection.Traversable[B])(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
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, butTraversable
and down can use the overload.- B
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 classRepr
, but this depends on the element typeB
being admissible for that class, which means that an implicit instance of typeCanBuildFrom[Repr, B, That]
is found.- that
the traversable to append.
- bf
an implicit value of class
CanBuildFrom
which determines the result classThat
from the current representation typeRepr
and the new element typeB
.- returns
a new collection of type
That
which contains all elements of this traversable collection followed by all elements ofthat
.
- Definition Classes
- TraversableLike
-
def
++:[B](that: TraversableOnce[B]): Traversable[B]
[use case] As with
++
, returns a new collection containing the elements from the left operand followed by the elements from the right operand.[use case]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)
- B
the element type of the returned collection.
- that
the traversable to append.
- returns
a new collection which contains all elements of this collection followed by all elements of
that
.
- Definition Classes
- TraversableLike
Full Signaturedef ++:[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
-
def
->[B](y: B): (Traversable[A], B)
- Implicit
- This member is added by an implicit conversion from Traversable[A] to ArrowAssoc[Traversable[A]] performed by method ArrowAssoc in scala.Predef.
- Definition Classes
- ArrowAssoc
- Annotations
- @inline()
-
final
def
==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.- returns
true
if the receiver object is equivalent to the argument;false
otherwise.
- Definition Classes
- AnyRef → Any
-
def
addString(b: scala.StringBuilder): scala.StringBuilder
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
- b
the string builder to which elements are appended.
- returns
the string builder
b
to which elements were appended.
- Definition Classes
- TraversableOnce
-
def
addString(b: scala.StringBuilder, sep: String): scala.StringBuilder
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 stringsep
.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
- b
the string builder to which elements are appended.
- sep
the separator string.
- returns
the string builder
b
to which elements were appended.
- Definition Classes
- TraversableOnce
-
def
addString(b: scala.StringBuilder, start: String, sep: String, end: String): scala.StringBuilder
Appends all elements of this traversable or iterator to a string builder using start, end, and separator strings.
Appends all elements of this traversable or iterator to a string builder using start, end, and separator strings. The written text begins with the string
start
and ends with the stringend
. Inside, the string representations (w.r.t. the methodtoString
) of all elements of this traversable or iterator are separated by the stringsep
.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 , "List(" , ", " , ")") res5: StringBuilder = List(1, 2, 3, 4)
- b
the string builder to which elements are appended.
- start
the starting string.
- sep
the separator string.
- end
the ending string.
- returns
the string builder
b
to which elements were appended.
- Definition Classes
- TraversableOnce
-
def
aggregate[B](z: ⇒ B)(seqop: (B, A) ⇒ B, combop: (B, B) ⇒ B): B
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
andreduce
. It is similar tofoldLeft
in that it doesn't require the result to be a supertype of the element type. In addition, it allows parallel collections to be processed in chunks, and then combines the intermediate results.aggregate
splits the traversable or iterator into partitions and processes each partition by sequentially applyingseqop
, starting withz
(likefoldLeft
). Those intermediate results are then combined by usingcombop
(likefold
). The implementation of this operation may operate on an arbitrary number of collection partitions (even 1), socombop
may be invoked an arbitrary number of times (even 0).As an example, consider summing up the integer values of a list of chars. The initial value for the sum is 0. First,
seqop
transforms each input character to an Int and adds it to the sum (of the partition). Then,combop
just needs to sum up the intermediate results of the partitions:List('a', 'b', 'c').aggregate(0)({ (sum, ch) => sum + ch.toInt }, { (p1, p2) => p1 + p2 })
- B
the type of accumulated results
- z
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 or0
for summation) and may be evaluated more than once- seqop
an operator used to accumulate results within a partition
- combop
an associative operator used to combine results from different partitions
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
final
def
asInstanceOf[T0]: T0
Cast the receiver object to be of type
T0
.Cast the receiver object to be of type
T0
.Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression
1.asInstanceOf[String]
will throw aClassCastException
at runtime, while the expressionList(1).asInstanceOf[List[String]]
will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastException
if the receiver object is not an instance of the erasure of typeT0
.
-
def
clone(): AnyRef
Create a copy of the receiver object.
-
def
collect[B](pf: PartialFunction[A, B]): Traversable[B]
[use case] Builds a new collection by applying a partial function to all elements of this collection on which the function is defined.
[use case]Builds a new collection by applying a partial function to all elements of this collection on which the function is defined.
- B
the element type of the returned collection.
- pf
the partial function which filters and maps the collection.
- returns
a new collection 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.
- Definition Classes
- TraversableLike → GenTraversableLike
Full Signaturedef collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
-
def
collectFirst[B](pf: PartialFunction[A, B]): Option[B]
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.
- pf
the partial function
- returns
an option value containing pf applied to the first value for which it is defined, or
None
if none exists.
- Definition Classes
- TraversableOnce
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
Example: -
def
companion: GenericCompanion[Traversable]
The factory companion object that builds instances of class Traversable.
The factory companion object that builds instances of class Traversable. (or its
Iterable
superclass where class Traversable is not aSeq
.)- Definition Classes
- Traversable → Traversable → GenTraversable → GenericTraversableTemplate
-
def
copyToArray(xs: Array[A], start: Int, len: Int): Unit
[use case] Copies the elements of this collection to an array.
[use case]Copies the elements of this collection to an array. Fills the given array
xs
with at mostlen
elements of this collection, starting at positionstart
. Copying will stop once either the end of the current collection is reached, or the end of the target array is reached, orlen
elements have been copied.Note: will not terminate for infinite-sized collections.
- xs
the array to fill.
- start
the starting index.
- len
the maximal number of elements to copy.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
-
def
copyToArray(xs: Array[A]): Unit
[use case] Copies the elements of this collection to an array.
[use case]Copies the elements of this collection to an array. Fills the given array
xs
with values of this collection. Copying will stop once either the end of the current collection is reached, or the end of the target array is reached.Note: will not terminate for infinite-sized collections.
- xs
the array to fill.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
copyToArray(xs: Array[A], start: Int): Unit
[use case] Copies the elements of this collection to an array.
[use case]Copies the elements of this collection to an array. Fills the given array
xs
with values of this collection, beginning at indexstart
. Copying will stop once either the end of the current collection is reached, or the end of the target array is reached.Note: will not terminate for infinite-sized collections.
- xs
the array to fill.
- start
the starting index.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
copyToBuffer[B >: A](dest: Buffer[B]): Unit
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.
- dest
The buffer to which elements are copied.
- Definition Classes
- TraversableOnce
-
def
count(p: (A) ⇒ Boolean): Int
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.
- p
the predicate used to test elements.
- returns
the number of elements satisfying the predicate
p
.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
drop(n: Int): Traversable[A]
Selects all elements except first n ones.
Selects all elements except first n ones.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- n
the number of elements to drop from this traversable collection.
- returns
a traversable collection consisting of all elements of this traversable collection except the first
n
ones, or else the empty traversable collection, if this traversable collection has less thann
elements. Ifn
is negative, don't drop any elements.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
dropWhile(p: (A) ⇒ Boolean): Traversable[A]
Drops longest prefix of elements that satisfy a predicate.
Drops longest prefix of elements that satisfy a predicate.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
the longest suffix of this traversable collection whose first element does not satisfy the predicate
p
.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
ensuring(cond: (Traversable[A]) ⇒ Boolean, msg: ⇒ Any): Traversable[A]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to Ensuring[Traversable[A]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
-
def
ensuring(cond: (Traversable[A]) ⇒ Boolean): Traversable[A]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to Ensuring[Traversable[A]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
-
def
ensuring(cond: Boolean, msg: ⇒ Any): Traversable[A]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to Ensuring[Traversable[A]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
-
def
ensuring(cond: Boolean): Traversable[A]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to Ensuring[Traversable[A]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
-
final
def
eq(arg0: AnyRef): Boolean
Tests whether the argument (
that
) is a reference to the receiver object (this
).Tests whether the argument (
that
) is a reference to the receiver object (this
).The
eq
method implements an equivalence relation on non-null instances ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2
), they should be equal to each other (o1 == o2
) and they should hash to the same value (o1.hashCode == o2.hashCode
).- returns
true
if the argument is a reference to the receiver object;false
otherwise.
- Definition Classes
- AnyRef
- It is consistent: for any non-null instances
-
def
equals(arg0: Any): Boolean
The equality method for reference types.
-
def
exists(p: (A) ⇒ Boolean): Boolean
Tests whether a predicate holds for at least one element of this traversable collection.
Tests whether a predicate holds for at least one element of this traversable collection.
Note: may not terminate for infinite-sized collections.
- p
the predicate used to test elements.
- returns
false
if this traversable collection is empty, otherwisetrue
if the given predicatep
holds for some of the elements of this traversable collection, otherwisefalse
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
-
def
filter(p: (A) ⇒ Boolean): Traversable[A]
Selects all elements of this traversable collection which satisfy a predicate.
Selects all elements of this traversable collection which satisfy a predicate.
- p
the predicate used to test elements.
- returns
a new traversable collection consisting of all elements of this traversable collection that satisfy the given predicate
p
. The order of the elements is preserved.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
filterNot(p: (A) ⇒ Boolean): Traversable[A]
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.
- p
the predicate used to test elements.
- returns
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.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the
finalize
method is invoked, as well as the interaction betweenfinalize
and non-local returns and exceptions, are all platform dependent.- Attributes
- protected[lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( classOf[java.lang.Throwable] )
- Note
not specified by SLS as a member of AnyRef
-
def
find(p: (A) ⇒ Boolean): Option[A]
Finds the first element of the traversable collection satisfying a predicate, if any.
Finds the first element of the traversable collection satisfying a predicate, if any.
Note: may not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- p
the predicate used to test elements.
- returns
an option value containing the first element in the traversable collection that satisfies
p
, orNone
if none exists.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
-
def
flatMap[B](f: (A) ⇒ GenTraversableOnce[B]): Traversable[B]
[use case] Builds a new collection by applying a function to all elements of this collection and using the elements of the resulting collections.
[use case]Builds a new collection by applying a function to all elements of this collection and using the elements of the resulting collections.
For example:
def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")
The type of the resulting collection is guided by the static type of collection. This might cause unexpected results sometimes. For example:
// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet) // lettersOf will return a Set[Char], not a Seq def lettersOf(words: Seq[String]) = words.toSet flatMap (word => word.toSeq) // xs will be an Iterable[Int] val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2) // ys will be a Map[Int, Int] val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)
- B
the element type of the returned collection.
- f
the function to apply to each element.
- returns
a new collection resulting from applying the given collection-valued function
f
to each element of this collection and concatenating the results.
- Definition Classes
- TraversableLike → GenTraversableLike → FilterMonadic
Full Signaturedef flatMap[B, That](f: (A) ⇒ GenTraversableOnce[B])(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
-
def
flatten[B]: Traversable[B]
[use case] Converts this collection of traversable collections into a collection formed by the elements of these traversable collections.
[use case]Converts this collection of traversable collections into a collection formed by the elements of these traversable 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(1, 2, 3) ).flatten // xs == List(1, 2, 3, 1, 2, 3) val ys = Set( List(1, 2, 3), List(3, 2, 1) ).flatten // ys == Set(1, 2, 3)
- B
the type of the elements of each traversable collection.
- returns
a new collection resulting from concatenating all element collections.
- Definition Classes
- GenericTraversableTemplate
Full Signaturedef flatten[B](implicit asTraversable: (A) ⇒ GenTraversableOnce[B]): Traversable[B]
-
def
fold[A1 >: A](z: A1)(op: (A1, A1) ⇒ A1): A1
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.
Note: will not terminate for infinite-sized collections.
- A1
a type parameter for the binary operator, a supertype of
A
.- z
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).- op
a binary operator that must be associative.
- returns
the result of applying the fold operator
op
between all the elements andz
, orz
if this traversable or iterator is empty.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
foldLeft[B](z: B)(op: (B, A) ⇒ B): B
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: 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.
- B
the result type of the binary operator.
- z
the start value.
- op
the binary operator.
- returns
the result of inserting
op
between consecutive elements of this traversable or iterator, going left to right with the start valuez
on the left:op(...op(z, x_1), x_2, ..., x_n)
where
x1, ..., xn
are the elements of this traversable or iterator. Returnsz
if this traversable or iterator is empty.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
foldRight[B](z: B)(op: (A, B) ⇒ B): B
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: 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.
- B
the result type of the binary operator.
- z
the start value.
- op
the binary operator.
- returns
the result of inserting
op
between consecutive elements of this traversable or iterator, going right to left with the start valuez
on the right:op(x_1, op(x_2, ... op(x_n, z)...))
where
x1, ..., xn
are the elements of this traversable or iterator. Returnsz
if this traversable or iterator is empty.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
forall(p: (A) ⇒ Boolean): Boolean
Tests whether a predicate holds for all elements of this traversable collection.
Tests whether a predicate holds for all elements of this traversable collection.
Note: may not terminate for infinite-sized collections.
- p
the predicate used to test elements.
- returns
true
if this traversable collection is empty or the given predicatep
holds for all elements of this traversable collection, otherwisefalse
.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
-
abstract
def
foreach(f: (A) ⇒ Unit): Unit
[use case]
[use case]- f
the function that is applied for its side-effect to every element. The result of function
f
is discarded.
- Definition Classes
- GenericTraversableTemplate
Full Signatureabstract def foreach[U](f: (A) ⇒ U): Unit
-
def
formatted(fmtstr: String): String
Returns string formatted according to given
format
string.Returns string formatted according to given
format
string. Format strings are as forString.format
(@see java.lang.String.format).- Implicit
- This member is added by an implicit conversion from Traversable[A] to StringFormat[Traversable[A]] performed by method StringFormat in scala.Predef.
- Definition Classes
- StringFormat
- Annotations
- @inline()
-
def
genericBuilder[B]: Builder[B, Traversable[B]]
The generic builder that builds instances of Traversable at arbitrary element types.
The generic builder that builds instances of Traversable at arbitrary element types.
- Definition Classes
- GenericTraversableTemplate
-
final
def
getClass(): Class[_]
Returns the runtime class representation of the object.
-
def
groupBy[K](f: (A) ⇒ K): immutable.Map[K, Traversable[A]]
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.
- K
the type of keys returned by the discriminator function.
- f
the discriminator function.
- returns
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 elementsx
for whichf(x)
equalsk
.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
hasDefiniteSize: Boolean
Tests whether this traversable collection is known to have a finite size.
Tests whether this traversable collection 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 returnstrue
if all elements have been computed. It returnsfalse
if the stream is not yet evaluated to the end. Non-empty Iterators usually returnfalse
even if they were created from a collection with a known finite size.Note: many collection methods will not work on collections of infinite sizes. The typical failure mode is an infinite loop. These methods always attempt a traversal without checking first that
hasDefiniteSize
returnstrue
. However, checkinghasDefiniteSize
can provide an assurance that size is well-defined and non-termination is not a concern.- returns
true
if this collection is known to have finite size,false
otherwise.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
-
def
hashCode(): Int
The hashCode method for reference types.
-
def
head: A
Selects the first element of this traversable collection.
Selects the first element of this traversable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
the first element of this traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
- Exceptions thrown
NoSuchElementException
if the traversable collection is empty.
-
def
headOption: Option[A]
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.
- returns
the first element of this traversable collection if it is nonempty,
None
if it is empty.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
init: Traversable[A]
Selects all elements except the last.
Selects all elements except the last.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
a traversable collection consisting of all elements of this traversable collection except the last one.
- Definition Classes
- TraversableLike → GenTraversableLike
- Exceptions thrown
UnsupportedOperationException
if the traversable collection is empty.
-
def
inits: Iterator[Traversable[A]]
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
.- returns
an iterator over all the inits of this traversable collection
- Definition Classes
- TraversableLike
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
Example: -
def
isEmpty: Boolean
Tests whether this traversable collection is empty.
Tests whether this traversable collection is empty.
- returns
true
if the traversable collection contain no elements,false
otherwise.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
-
final
def
isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is
T0
.Test whether the dynamic type of the receiver object is
T0
.Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression
1.isInstanceOf[String]
will returnfalse
, while the expressionList(1).isInstanceOf[List[String]]
will returntrue
. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
-
final
def
isTraversableAgain: Boolean
Tests whether this traversable collection can be repeatedly traversed.
Tests whether this traversable collection can be repeatedly traversed.
- returns
true
- Definition Classes
- TraversableLike → GenTraversableLike → GenTraversableOnce
-
def
last: A
Selects the last element.
Selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
The last element of this traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
- Exceptions thrown
NoSuchElementException
If the traversable collection is empty.
-
def
lastOption: Option[A]
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.
- returns
the last element of this traversable collection$ if it is nonempty,
None
if it is empty.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
map[B](f: (A) ⇒ B): Traversable[B]
[use case] Builds a new collection by applying a function to all elements of this collection.
[use case]Builds a new collection by applying a function to all elements of this collection.
- B
the element type of the returned collection.
- f
the function to apply to each element.
- returns
a new collection resulting from applying the given function
f
to each element of this collection and collecting the results.
- Definition Classes
- TraversableLike → GenTraversableLike → FilterMonadic
Full Signaturedef map[B, That](f: (A) ⇒ B)(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
-
def
max: A
[use case] Finds the largest element.
[use case]Finds the largest element.
- returns
the largest element of this collection.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this collection is empty.
Full Signaturedef max[B >: A](implicit cmp: Ordering[B]): A
-
def
maxBy[B](f: (A) ⇒ B): A
[use case] Finds the first element which yields the largest value measured by function f.
[use case]Finds the first element which yields the largest value measured by function f.
- B
The result type of the function f.
- f
The measuring function.
- returns
the first element of this collection with the largest value measured by function f.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this collection is empty.
Full Signaturedef maxBy[B](f: (A) ⇒ B)(implicit cmp: Ordering[B]): A
-
def
min: A
[use case] Finds the smallest element.
[use case]Finds the smallest element.
- returns
the smallest element of this collection
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this collection is empty.
Full Signaturedef min[B >: A](implicit cmp: Ordering[B]): A
-
def
minBy[B](f: (A) ⇒ B): A
[use case] Finds the first element which yields the smallest value measured by function f.
[use case]Finds the first element which yields the smallest value measured by function f.
- B
The result type of the function f.
- f
The measuring function.
- returns
the first element of this collection with the smallest value measured by function f.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this collection is empty.
Full Signaturedef minBy[B](f: (A) ⇒ B)(implicit cmp: Ordering[B]): A
-
def
mkString: String
Displays all elements of this traversable or iterator in a string.
Displays all elements of this traversable or iterator in a string.
- returns
a string representation of this traversable or iterator. In the resulting string the string representations (w.r.t. the method
toString
) of all elements of this traversable or iterator follow each other without any separator string.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
mkString(sep: String): String
Displays all elements of this traversable or iterator in a string using a separator string.
Displays all elements of this traversable or iterator in a string using a separator string.
- sep
the separator string.
- returns
a string representation of this traversable or iterator. In the resulting string the string representations (w.r.t. the method
toString
) of all elements of this traversable or iterator are separated by the stringsep
.
- Definition Classes
- TraversableOnce → GenTraversableOnce
List(1, 2, 3).mkString("|") = "1|2|3"
Example: -
def
mkString(start: String, sep: String, end: String): String
Displays all elements of this traversable or iterator in a string using start, end, and separator strings.
Displays all elements of this traversable or iterator in a string using start, end, and separator strings.
- start
the starting string.
- sep
the separator string.
- end
the ending string.
- returns
a string representation of this traversable or iterator. The resulting string begins with the string
start
and ends with the stringend
. Inside, the string representations (w.r.t. the methodtoString
) of all elements of this traversable or iterator are separated by the stringsep
.
- Definition Classes
- TraversableOnce → GenTraversableOnce
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Example: -
final
def
ne(arg0: AnyRef): Boolean
Equivalent to
!(this eq that)
.Equivalent to
!(this eq that)
.- returns
true
if the argument is not a reference to the receiver object;false
otherwise.
- Definition Classes
- AnyRef
-
def
newBuilder: Builder[A, Traversable[A]]
The builder that builds instances of type Traversable[A]
The builder that builds instances of type Traversable[A]
- Attributes
- protected[this]
- Definition Classes
- GenericTraversableTemplate → HasNewBuilder
-
def
nonEmpty: Boolean
Tests whether the traversable or iterator is not empty.
Tests whether the traversable or iterator is not empty.
- returns
true
if the traversable or iterator contains at least one element,false
otherwise.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
final
def
notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
-
final
def
notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
-
def
par: ParIterable[A]
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
ormutable.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.
- returns
a parallel implementation of this collection
- Definition Classes
- Parallelizable
-
def
parCombiner: Combiner[A, ParIterable[A]]
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.- returns
a combiner for the parallel collection of type
ParRepr
- Attributes
- protected[this]
- Definition Classes
- TraversableLike → Parallelizable
-
def
partition(p: (A) ⇒ Boolean): (Traversable[A], Traversable[A])
Partitions this traversable collection in two traversable collections according to a predicate.
Partitions this traversable collection in two traversable collections according to a predicate.
- p
the predicate on which to partition.
- returns
a pair of traversable collections: the first traversable collection consists of all elements that satisfy the predicate
p
and the second traversable collection consists of all elements that don't. The relative order of the elements in the resulting traversable collections is the same as in the original traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
product: A
[use case] Multiplies up the elements of this collection.
[use case]Multiplies up the elements of this collection.
- returns
the product of all elements in this collection of numbers of type
Int
. Instead ofInt
, any other typeT
with an implicitNumeric[T]
implementation can be used as element type of the collection and as result type ofproduct
. Examples of such types are:Long
,Float
,Double
,BigInt
.
- Definition Classes
- TraversableOnce → GenTraversableOnce
Full Signaturedef product[B >: A](implicit num: Numeric[B]): B
-
def
reduce[A1 >: A](op: (A1, A1) ⇒ A1): A1
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.
- A1
A type parameter for the binary operator, a supertype of
A
.- op
A binary operator that must be associative.
- returns
The result of applying reduce operator
op
between all the elements if the traversable or iterator is nonempty.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this traversable or iterator is empty.
-
def
reduceLeft[B >: A](op: (B, A) ⇒ B): B
Applies a binary operator to all elements of this traversable or iterator, going left to right.
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.
- B
the result type of the binary operator.
- op
the binary operator.
- returns
the result of inserting
op
between consecutive elements of this traversable or iterator, going left to right:op( op( ... op(x_1, x_2) ..., x_{n-1}), x_n)
where
x1, ..., xn
are the elements of this traversable or iterator.
- Definition Classes
- TraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this traversable or iterator is empty.
-
def
reduceLeftOption[B >: A](op: (B, A) ⇒ B): Option[B]
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.
- B
the result type of the binary operator.
- op
the binary operator.
- returns
an option value containing the result of
reduceLeft(op)
if this traversable or iterator is nonempty,None
otherwise.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
reduceOption[A1 >: A](op: (A1, A1) ⇒ A1): Option[A1]
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.
- A1
A type parameter for the binary operator, a supertype of
A
.- op
A binary operator that must be associative.
- returns
An option value containing result of applying reduce operator
op
between all the elements if the collection is nonempty, andNone
otherwise.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
reduceRight[B >: A](op: (A, B) ⇒ B): B
Applies a binary operator to all elements of this traversable or iterator, going right to left.
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.
- B
the result type of the binary operator.
- op
the binary operator.
- returns
the result of inserting
op
between consecutive elements of this traversable or iterator, going right to left:op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
where
x1, ..., xn
are the elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Exceptions thrown
UnsupportedOperationException
if this traversable or iterator is empty.
-
def
reduceRightOption[B >: A](op: (A, B) ⇒ B): Option[B]
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.
- B
the result type of the binary operator.
- op
the binary operator.
- returns
an option value containing the result of
reduceRight(op)
if this traversable or iterator is nonempty,None
otherwise.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
repr: Traversable[A]
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 theTraversableLike
object itself, but this can be overridden.- Definition Classes
- TraversableLike → GenTraversableLike
-
def
reversed: List[A]
- Attributes
- protected[this]
- Definition Classes
- TraversableOnce
-
def
scan[B >: A, That](z: B)(op: (B, B) ⇒ B)(implicit cbf: CanBuildFrom[Traversable[A], B, That]): That
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.- B
element type of the resulting collection
- That
type of the resulting collection
- z
neutral element for the operator
op
- op
the associative operator for the scan
- cbf
combiner factory which provides a combiner
- returns
a new traversable collection containing the prefix scan of the elements in this traversable collection
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
scanLeft[B, That](z: B)(op: (B, A) ⇒ B)(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
Produces a collection containing cumulative results of applying the operator going left to right.
Produces a collection containing cumulative results of applying the operator 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.
- B
the type of the elements in the resulting collection
- That
the actual type of the resulting collection
- z
the initial value
- op
the binary operator applied to the intermediate result and the element
- bf
an implicit value of class
CanBuildFrom
which determines the result classThat
from the current representation typeRepr
and the new element typeB
.- returns
collection with intermediate results
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
scanRight[B, That](z: B)(op: (A, B) ⇒ B)(implicit bf: CanBuildFrom[Traversable[A], B, That]): That
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)
- B
the type of the elements in the resulting collection
- That
the actual type of the resulting collection
- z
the initial value
- op
the binary operator applied to the intermediate result and the element
- bf
an implicit value of class
CanBuildFrom
which determines the result classThat
from the current representation typeRepr
and the new element typeB
.- returns
collection with intermediate results
- Definition Classes
- TraversableLike → GenTraversableLike
- Annotations
- @migration
- Migration
(Changed in version 2.9.0) The behavior of
scanRight
has changed. The previous behavior can be reproduced with scanRight.reverse.
-
def
seq: Traversable[A]
A version of this collection with all of the operations implemented sequentially (i.e., in a single-threaded manner).
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.
- returns
a sequential view of the collection.
- Definition Classes
- Traversable → Traversable → GenTraversable → Parallelizable → TraversableOnce → GenTraversableOnce
-
def
size: Int
The size of this traversable or iterator.
The size of this traversable or iterator.
Note: will not terminate for infinite-sized collections.
- returns
the number of elements in this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
sizeHintIfCheap: Int
The size of this collection or iterator, if it can be cheaply computed
The size of this collection or iterator, if it can be cheaply computed
- returns
the number of elements in this collection or iterator, or -1 if the size cannot be determined cheaply
- Attributes
- protected[collection]
- Definition Classes
- GenTraversableOnce
-
def
slice(from: Int, until: Int): Traversable[A]
Selects an interval of elements.
Selects an interval of elements. The returned collection is made up of all elements
x
which satisfy the invariant:from <= indexOf(x) < until
Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
a traversable collection containing the elements greater than or equal to index
from
extending up to (but not including) indexuntil
of this traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
span(p: (A) ⇒ Boolean): (Traversable[A], Traversable[A])
Splits this traversable collection into a prefix/suffix pair according to a predicate.
Splits this traversable collection 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 predicatep
does not cause any side-effects.Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
a pair consisting of the longest prefix of this traversable collection whose elements all satisfy
p
, and the rest of this traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
splitAt(n: Int): (Traversable[A], Traversable[A])
Splits this traversable collection into two at a given position.
Splits this traversable collection into two at a given position. Note:
c splitAt n
is equivalent to (but possibly more efficient than)(c take n, c drop n)
.Note: might return different results for different runs, unless the underlying collection type is ordered.
- n
the position at which to split.
- returns
a pair of traversable collections consisting of the first
n
elements of this traversable collection, and the other elements.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
stringPrefix: String
Defines the prefix of this object's
toString
representation.Defines the prefix of this object's
toString
representation.- returns
a string representation which starts the result of
toString
applied to this traversable collection. By default the string prefix is the simple name of the collection class traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
sum: A
[use case] Sums up the elements of this collection.
[use case]Sums up the elements of this collection.
- returns
the sum of all elements in this collection of numbers of type
Int
. Instead ofInt
, any other typeT
with an implicitNumeric[T]
implementation can be used as element type of the collection and as result type ofsum
. Examples of such types are:Long
,Float
,Double
,BigInt
.
- Definition Classes
- TraversableOnce → GenTraversableOnce
Full Signaturedef sum[B >: A](implicit num: Numeric[B]): B
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
def
tail: Traversable[A]
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.
- returns
a traversable collection consisting of all elements of this traversable collection except the first one.
- Definition Classes
- TraversableLike → GenTraversableLike
- Exceptions thrown
java.lang.UnsupportedOperationException
if the traversable collection is empty.
-
def
tails: Iterator[Traversable[A]]
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
.- returns
an iterator over all the tails of this traversable collection
- Definition Classes
- TraversableLike
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Example: -
def
take(n: Int): Traversable[A]
Selects first n elements.
Selects first n elements.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- n
the number of elements to take from this traversable collection.
- returns
a traversable collection consisting only of the first
n
elements of this traversable collection, or else the whole traversable collection, if it has less thann
elements. Ifn
is negative, returns an empty traversable collection.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
takeWhile(p: (A) ⇒ Boolean): Traversable[A]
Takes longest prefix of elements that satisfy a predicate.
Takes longest prefix of elements that satisfy a predicate.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- returns
the longest prefix of this traversable collection whose elements all satisfy the predicate
p
.
- Definition Classes
- TraversableLike → GenTraversableLike
-
def
thisCollection: collection.Traversable[A]
The underlying collection seen as an instance of
Traversable
.The underlying collection seen as an instance of
Traversable
. By default this is implemented as the current collection object itself, but this can be overridden.- Attributes
- protected[this]
- Definition Classes
- TraversableLike
-
def
to[Col[_]]: Col[A]
[use case] Converts this collection into another by copying all elements.
[use case]Converts this collection into another by copying all elements.
Note: will not terminate for infinite-sized collections.
- Col
The collection type to build.
- returns
a new collection containing all elements of this collection.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
Full Signaturedef to[Col[_]](implicit cbf: CanBuildFrom[Nothing, A, Col[A]]): Col[A]
-
def
toArray: Array[A]
[use case] Converts this collection to an array.
[use case]Converts this collection to an array.
Note: will not terminate for infinite-sized collections.
- returns
an array containing all elements of this collection. An
ClassTag
must be available for the element type of this collection.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toBuffer[B >: A]: Buffer[B]
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.
- returns
a buffer containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toCollection(repr: Traversable[A]): collection.Traversable[A]
A conversion from collections of type
Repr
toTraversable
objects.A conversion from collections of type
Repr
toTraversable
objects. By default this is implemented as just a cast, but this can be overridden.- Attributes
- protected[this]
- Definition Classes
- TraversableLike
-
def
toIndexedSeq: immutable.IndexedSeq[A]
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.
- returns
an indexed sequence containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toIterable: collection.Iterable[A]
Converts this traversable or iterator to an iterable collection.
Converts this traversable or iterator to an iterable collection. Note that the choice of target
Iterable
is lazy in this default implementation as thisTraversableOnce
may be lazy and unevaluated (i.e. it may be an iterator which is only traversable once).Note: will not terminate for infinite-sized collections.
- returns
an
Iterable
containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toIterator: Iterator[A]
Returns an Iterator over the elements in this traversable collection.
Returns an Iterator over the elements in this traversable collection. Will return the same Iterator if this instance is already an Iterator.
Note: will not terminate for infinite-sized collections.
- returns
an Iterator containing all elements of this traversable collection.
- Definition Classes
- TraversableLike → GenTraversableOnce
-
def
toList: List[A]
Converts this traversable or iterator to a list.
Converts this traversable or iterator to a list.
Note: will not terminate for infinite-sized collections.
- returns
a list containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toMap[T, U]: collection.Map[T, U]
[use case] Converts this collection to a map.
[use case]Converts this collection 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.
- returns
a map of type
immutable.Map[T, U]
containing all key/value pairs of type(T, U)
of this collection.
- Definition Classes
- TraversableOnce → GenTraversableOnce
Full Signaturedef toMap[T, U](implicit ev: <:<[A, (T, U)]): immutable.Map[T, U]
-
def
toParArray: ParArray[T]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to CollectionsHaveToParArray[Traversable[A], T] performed by method CollectionsHaveToParArray in scala.collection.parallel. This conversion will take place only if an implicit value of type (Traversable[A]) ⇒ GenTraversableOnce[T] is in scope.
- Definition Classes
- CollectionsHaveToParArray
-
def
toSeq: collection.Seq[A]
Converts this traversable or iterator to a sequence.
Converts this traversable or iterator to a sequence. As with
toIterable
, it's lazy in this default implementation, as thisTraversableOnce
may be lazy and unevaluated.Note: will not terminate for infinite-sized collections.
- returns
a sequence containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toSet[B >: A]: immutable.Set[B]
Converts this traversable or iterator to a set.
Converts this traversable or iterator to a set.
Note: will not terminate for infinite-sized collections.
- returns
a set containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
toStream: Stream[A]
Converts this traversable collection to a stream.
Converts this traversable collection to a stream.
- returns
a stream containing all elements of this traversable collection.
- Definition Classes
- TraversableLike → GenTraversableOnce
-
def
toString(): String
Converts this traversable collection to a string.
Converts this traversable collection to a string.
- returns
a string representation of this collection. By default this string consists of the
stringPrefix
of this traversable collection, followed by all elements separated by commas and enclosed in parentheses.
- Definition Classes
- TraversableLike → Any
-
def
toTraversable: collection.Traversable[A]
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.
- returns
a Traversable containing all elements of this traversable collection.
- Definition Classes
- TraversableLike → TraversableOnce → GenTraversableOnce
- Annotations
- @deprecatedOverriding( message = ... , since = "2.11.0" )
-
def
toVector: Vector[A]
Converts this traversable or iterator to a Vector.
Converts this traversable or iterator to a Vector.
Note: will not terminate for infinite-sized collections.
- returns
a vector containing all elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
-
def
transpose[B](implicit asTraversable: (A) ⇒ GenTraversableOnce[B]): Traversable[Traversable[B]]
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))
- B
the type of the elements of each traversable collection.
- asTraversable
an implicit conversion which asserts that the element type of this collection is a
Traversable
.- returns
a two-dimensional collection of collections which has as nth row the nth column of this collection.
- Definition Classes
- GenericTraversableTemplate
- Annotations
- @migration
- Migration
(Changed in version 2.9.0)
transpose
throws anIllegalArgumentException
if collections are not uniformly sized.- Exceptions thrown
IllegalArgumentException
if all collections in this collection are not of the same size.
-
def
unzip[A1, A2](implicit asPair: (A) ⇒ (A1, A2)): (Traversable[A1], Traversable[A2])
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 = Traversable( (1, "one"), (2, "two"), (3, "three")).unzip // xs == (Traversable(1, 2, 3), // Traversable(one, two, three))
- A1
the type of the first half of the element pairs
- A2
the type of the second half of the element pairs
- asPair
an implicit conversion which asserts that the element type of this collection is a pair.
- returns
a pair of collections, containing the first, respectively second half of each element pair of this collection.
- Definition Classes
- GenericTraversableTemplate
-
def
unzip3[A1, A2, A3](implicit asTriple: (A) ⇒ (A1, A2, A3)): (Traversable[A1], Traversable[A2], Traversable[A3])
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 = Traversable( (1, "one", '1'), (2, "two", '2'), (3, "three", '3')).unzip3 // xs == (Traversable(1, 2, 3), // Traversable(one, two, three), // Traversable(1, 2, 3))
- A1
the type of the first member of the element triples
- A2
the type of the second member of the element triples
- A3
the type of the third member of the element triples
- asTriple
an implicit conversion which asserts that the element type of this collection is a triple.
- returns
a triple of collections, containing the first, second, respectively third member of each element triple of this collection.
- Definition Classes
- GenericTraversableTemplate
-
def
view(from: Int, until: Int): TraversableView[A, Traversable[A]]
Creates a non-strict view of a slice of this traversable collection.
Creates a non-strict view of a slice of this traversable collection.
Note: the difference between
view
andslice
is thatview
produces a view of the current traversable collection, whereasslice
produces a new traversable collection.Note:
view(from, to)
is equivalent toview.slice(from, to)
Note: might return different results for different runs, unless the underlying collection type is ordered.
- from
the index of the first element of the view
- until
the index of the element following the view
- returns
a non-strict view of a slice of this traversable collection, starting at index
from
and extending up to (but not including) indexuntil
.
- Definition Classes
- TraversableLike
-
def
view: TraversableView[A, Traversable[A]]
Creates a non-strict view of this traversable collection.
Creates a non-strict view of this traversable collection.
- returns
a non-strict view of this traversable collection.
- Definition Classes
- TraversableLike
-
final
def
wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
- final def wait(arg0: Long): Unit
-
def
withFilter(p: (A) ⇒ Boolean): FilterMonadic[A, Traversable[A]]
Creates a non-strict filter of this traversable collection.
Creates a non-strict filter of this traversable collection.
Note: the difference between
c filter p
andc withFilter p
is that the former creates a new collection, whereas the latter only restricts the domain of subsequentmap
,flatMap
,foreach
, andwithFilter
operations.Note: might return different results for different runs, unless the underlying collection type is ordered.
- p
the predicate used to test elements.
- returns
an object of class
WithFilter
, which supportsmap
,flatMap
,foreach
, andwithFilter
operations. All these operations apply to those elements of this traversable collection which satisfy the predicatep
.
- Definition Classes
- TraversableLike → FilterMonadic
-
def
→[B](y: B): (Traversable[A], B)
- Implicit
- This member is added by an implicit conversion from Traversable[A] to ArrowAssoc[Traversable[A]] performed by method ArrowAssoc in scala.Predef.
- Definition Classes
- ArrowAssoc
Shadowed Implicit Value Members
-
def
filter(p: (A) ⇒ Boolean): TraversableOnce[A]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to MonadOps[A] performed by method MonadOps in scala.collection.TraversableOnce.
- Shadowing
- This implicitly inherited member is shadowed by one or more members in this class.
To access this member you can use a type ascription:(traversable: MonadOps[A]).filter(p)
- Definition Classes
- MonadOps
-
def
flatMap[B](f: (A) ⇒ GenTraversableOnce[B]): TraversableOnce[B]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to MonadOps[A] performed by method MonadOps in scala.collection.TraversableOnce.
- Shadowing
- This implicitly inherited member is shadowed by one or more members in this class.
To access this member you can use a type ascription:(traversable: MonadOps[A]).flatMap(f)
- Definition Classes
- MonadOps
-
def
map[B](f: (A) ⇒ B): TraversableOnce[B]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to MonadOps[A] performed by method MonadOps in scala.collection.TraversableOnce.
- Shadowing
- This implicitly inherited member is shadowed by one or more members in this class.
To access this member you can use a type ascription:(traversable: MonadOps[A]).map(f)
- Definition Classes
- MonadOps
-
def
withFilter(p: (A) ⇒ Boolean): Iterator[A]
- Implicit
- This member is added by an implicit conversion from Traversable[A] to MonadOps[A] performed by method MonadOps in scala.collection.TraversableOnce.
- Shadowing
- This implicitly inherited member is shadowed by one or more members in this class.
To access this member you can use a type ascription:(traversable: MonadOps[A]).withFilter(p)
- Definition Classes
- MonadOps
Deprecated Value Members
-
def
/:[B](z: B)(op: (B, A) ⇒ B): B
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 forfoldLeft
;z /: xs
is the same asxs 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.
- B
the result type of the binary operator.
- z
the start value.
- op
the binary operator.
- returns
the result of inserting
op
between consecutive elements of this traversable or iterator, going left to right with the start valuez
on the left:op(...op(op(z, x_1), x_2), ..., x_n)
where
x1, ..., xn
are the elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Annotations
- @deprecated
- Deprecated
(Since version 2.12.10) Use foldLeft instead of /:
-
def
:\[B](z: B)(op: (A, B) ⇒ B): B
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 forfoldRight
;xs :\ z
is the same asxs 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
- B
the result type of the binary operator.
- z
the start value
- op
the binary operator
- returns
the result of inserting
op
between consecutive elements of this traversable or iterator, going right to left with the start valuez
on the right:op(x_1, op(x_2, ... op(x_n, z)...))
where
x1, ..., xn
are the elements of this traversable or iterator.
- Definition Classes
- TraversableOnce → GenTraversableOnce
- Annotations
- @deprecated
- Deprecated
(Since version 2.12.10) Use foldRight instead of :\
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.collection.parallel.immutable
- Immutable, parallel data-structures such asParVector
,ParRange
,ParHashMap
orParHashSet
scala.collection.parallel.mutable
- Mutable, parallel data-structures such asParArray
,ParHashMap
,ParTrieMap
orParHashSet
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.