the first element of the list
the list containing the remaining elements of this list after the first one.
A class supporting filtered operations. Instances of this class are returned by method withFilter
.
The type implementing this traversable
Test two objects for inequality.
true
if !(this == that), false otherwise.
Equivalent to x.hashCode
except for boxed numeric types and null
. 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. For null
returns a hashcode where null.hashCode
throws a NullPointerException
.
a hash value consistent with ==
Returns a new list containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the list is the most specific superclass encompassing the element types of the two operands.
the element type of the returned collection.
the class of the returned collection. In the standard library configuration, That
is always List[B]
because an implicit of type CanBuildFrom[List, B, That]
is defined in object List
.
the traversable to append.
an implicit value of class CanBuildFrom
which determines the result class That
from the current representation type Repr
and the new element type B
. This is usually the canBuildFrom
value defined in object List
.
a new collection of type That
which contains all elements of this list followed by all elements of that
.
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 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
.
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 list which contains all elements of this list followed by all elements of that
.
A copy of the list 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 list 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 list consisting of elem
followed by all elements of this list.
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.
A copy of this list with an element appended.
A mnemonic for +:
vs. :+
is: the COLon goes on the COLlection side.
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 list consisting of all elements of this list followed by elem
.
Adds an element at the beginning of this list.
Example:
1 :: List(2, 3) = List(2, 3).::(1) = List(1, 2, 3)
the element to prepend.
a list which contains x
as first element and which continues with this list.
Adds the elements of a given list in front of this list.
Example:
List(1, 2) ::: List(3, 4) = List(3, 4).:::(List(1, 2)) = List(1, 2, 3, 4)
The list elements to prepend.
a list resulting from the concatenation of the given list prefix
and this list.
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.
The expression x == that
is equivalent to if (x eq null) that eq null else x.equals(that)
.
true
if the receiver object is equivalent to the argument; false
otherwise.
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. 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.
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 string end
. Inside, the string representations (w.r.t. the method toString
) of all elements of this traversable or iterator are 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 , "List(" , ", " , ")") res5: StringBuilder = List(1, 2, 3, 4)
the string builder to which elements are appended.
the starting string.
the separator string.
the ending string.
the string builder b
to which elements were appended.
Aggregates the results of applying an operator to subsequent elements.
This is a more general form of fold
and reduce
. It is similar to foldLeft
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 applying seqop
, starting with z
(like foldLeft
). Those intermediate results are then combined by using combop
(like fold
). The implementation of this operation may operate on an arbitrary number of collection partitions (even 1), so combop
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 })
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.
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))
.
Selects an element by its index in the sequence. Note: the execution of apply
may take time proportional to the index value.
the element of this sequence at index idx
, where 0
indicates the first element.
IndexOutOfBoundsException
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 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
evaluation
lift
and unlift
do not evaluate source functions twice on each invocation
runWith
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
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 a ClassCastException
at runtime, while the expression List(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.
the receiver object.
ClassCastException
if the receiver object is not an instance of the erasure of type T0
.
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.
Create a copy of the receiver object.
The default implementation of the clone
method is platform dependent.
a copy of the receiver object.
Builds a new collection by applying a partial function to all elements of this list on which the function is defined.
the element type of the returned collection.
the partial function which filters and maps the list.
a new list 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.
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. A _combination_ of length n
is a subsequence of the original sequence, with the elements taken in order. Thus, "xy"
and "yy"
are both length-2 combinations of "xyy"
, but "yx"
is not. If there is more than one way to generate the same subsequence, only one will be returned.
For example, "xyyy"
has three different ways to generate "xy"
depending on whether the first, second, or third "y"
is selected. However, since all are identical, only one will be chosen. Which of the three will be taken is an implementation detail that is not defined.
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 List
. (or its Iterable
superclass where class List
is not a Seq
.)
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.
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.
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
.
Copies the elements of this list to an array. Fills the given array xs
with at most len
elements of this list, starting at position start
. Copying will stop once either the end of the current list is reached, or the end of the target array is reached, or len
elements have been copied.
the array to fill.
the starting index.
the maximal number of elements to copy.
Copies the elements of this list to an array. Fills the given array xs
with values of this list. Copying will stop once either the end of the current list is reached, or the end of the target array is reached.
the array to fill.
Copies the elements of this list to an array. Fills the given array xs
with values of this list, beginning at index start
. Copying will stop once either the end of the current list is reached, or the end of the target array is reached.
the array to fill.
the starting index.
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.
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.
the predicate used to test elements.
the number of elements satisfying the predicate p
.
Computes the multiset difference between this list and another sequence.
the sequence of elements to remove
a new list which contains all elements of this list 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 sequence from this sequence without any duplicate elements.
Note: will not terminate for infinite-sized collections.
A new sequence which contains the first occurrence of every element of this sequence.
Selects all elements except first n ones.
the number of elements to drop from this list.
a list consisting of all elements of this list except the first n
ones, or else the empty list, if this list has less than n
elements. If n
is negative, don't drop any elements.
Selects all elements except last n ones.
The number of elements to take
a sequence consisting of all elements of this sequence except the last n
ones, or else the empty sequence, if this sequence has less than n
elements.
Drops longest prefix of elements that satisfy a predicate.
the longest suffix of this list whose first element does not satisfy the predicate p
.
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.
Tests whether the argument (that
) is a reference to the receiver object (this
).
The eq
method implements an equivalence relation on non-null instances of AnyRef
, and has three additional properties:
x
and y
of type AnyRef
, multiple invocations of x.eq(y)
consistently returns true
or consistently returns false
.For any non-null instance x
of type AnyRef
, x.eq(null)
and null.eq(x)
returns false
.
null.eq(null)
returns true
. When overriding the equals
or hashCode
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
).
true
if the argument is a reference to the receiver object; false
otherwise.
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 at least one element 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
Selects all elements of this traversable collection which satisfy a predicate.
the predicate used to test elements.
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.
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.
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 between finalize
and non-local returns and exceptions, are all platform dependent.
not specified by SLS as a member of AnyRef
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.
Builds a new collection by applying a function to all elements of this list 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 list. 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)
the element type of the returned collection.
the function to apply to each element.
a new list resulting from applying the given collection-valued function f
to each element of this list and concatenating the results.
Converts this list of traversable collections into a list formed by the elements of these traversable collections.
The resulting collection's type will be guided by the static type of list. 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)
the type of the elements of each traversable collection.
a new list resulting from concatenating all element lists.
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.
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 the fold operator op
between all the elements and z
, or z
if this traversable or iterator is empty.
Applies a binary operator to a start value and all elements of this sequence, going left to right.
Note: will not terminate for infinite-sized collections.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this sequence, going left to right with the start value z
on the left:
op(...op(z, x_1), x_2, ..., x_n)
where x_{1}, ..., x_{n}
are the elements of this sequence. Returns z
if this sequence is empty.
Applies a binary operator to all elements of this list and a start value, going right to left.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this list, 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 list. Returns z
if this list is empty.
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 or the given predicate p
holds for all elements of this sequence, otherwise false
.
Applies a function f
to all elements of this list.
Note: this method underlies the implementation of most other bulk operations. Subclasses should re-implement this method if a more efficient implementation exists.
the function that is applied for its side-effect to every element. The result of function f
is discarded.
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 Traversable at arbitrary element types.
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
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.
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 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 returns true
if all elements have been computed. It returns false
if the stream is not yet evaluated to the end. Non-empty Iterators usually return false
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
returns true
. However, checking hasDefiniteSize
can provide an assurance that size is well-defined and non-termination is not a concern.
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.
the hash code value for this object.
Selects the first element of this list.
the first element of this list.
NoSuchElementException
if the list is empty.
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.
Finds index of first occurrence of some value in this list after or at some start index.
the element value to search for.
the start index
the index >= from
of the first element of this list that is equal (as determined by ==
) to elem
, or -1
, if none exists.
Finds index of first occurrence of some value in this list.
the element value to search for.
the index of the first element of this list 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.
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.
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.
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.
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.
a Range
value from 0
to one less than the length of this sequence.
Selects all elements except the last.
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 last one.
UnsupportedOperationException
if the traversable collection is empty.
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)
Computes the multiset intersection between this list and another sequence.
the sequence of elements to intersect with.
a new list which contains all elements of this list 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.
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 the list is empty.
Note: Implementations in subclasses that are not repeatedly traversable must take care not to consume any elements when isEmpty
is called.
true
if the list contains no elements, false
otherwise.
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 return false
, while the expression List(1).isInstanceOf[List[String]]
will return true
. 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.
true
if the receiver object is an instance of erasure of type T0
; false
otherwise.
Tests whether this traversable collection can be repeatedly traversed.
true
Creates a new iterator over all elements contained in this iterable object.
the new iterator
Selects the last element.
The last element of this sequence.
NoSuchElementException
If the sequence is empty.
Finds index of last occurrence of some value in this list 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 list that is equal (as determined by ==
) to elem
, or -1
, if none exists.
Finds index of last occurrence of some value in this list.
the element value to search for.
the index of the last element of this list 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.
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.
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.
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.
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.
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.
The length of the sequence.
Note: will not terminate for infinite-sized collections.
Note: the execution of length
may take time proportional to the length of the sequence.
the number of elements in this sequence.
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.
a function that takes an argument x
to Some(this(x))
if this
is defined for x
, and to None
otherwise.
Function.unlift
Builds a new collection by applying a function to all elements of this list.
the element type of the returned collection.
the function to apply to each element.
a new list resulting from applying the given function f
to each element of this list and collecting the results.
Builds a new list by applying a function to all elements of this list. Like xs map f
, but returns xs
unchanged if function f
maps all elements to themselves (as determined by eq
).
the function to apply to each element.
a list resulting from applying the given function f
to each element of this list and collecting the results.
Finds the largest element.
the largest element of this list.
UnsupportedOperationException
if this list is empty.
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 list with the largest value measured by function f.
UnsupportedOperationException
if this list is empty.
Finds the smallest element.
the smallest element of this list
UnsupportedOperationException
if this list is empty.
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 list with the smallest value measured by function f.
UnsupportedOperationException
if this list is empty.
Displays all elements of this traversable or iterator in a string.
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.
Displays all elements of this traversable or iterator in a string using a separator string.
the separator string.
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 string sep
.
List(1, 2, 3).mkString("|") = "1|2|3"
Displays all elements of this traversable or iterator in a string using start, end, and separator strings.
the starting string.
the separator string.
the ending string.
a string representation of this traversable or iterator. 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 traversable or iterator are separated by the string sep
.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Equivalent to !(this eq that)
.
true
if the argument is not a reference to the receiver object; false
otherwise.
The builder that builds instances of type Traversable[A]
Tests whether the traversable or iterator is not empty.
true
if the traversable or iterator contains at least one element, false
otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
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.
A copy of this list with an element value appended until a given target length is reached.
the target length
the padding value
a new list consisting of all elements of this list followed by the minimal number of occurrences of elem
so that the resulting list has a length of at least len
.
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.
a combiner for the parallel collection of type ParRepr
Partitions this traversable collection in two traversable collections according to a predicate.
the predicate on which to partition.
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.
Produces a new list where a slice of elements in this list is replaced by another sequence.
the index of the first replaced element
the number of elements to drop in the original list
a new list consisting of all elements of this list except that replaced
elements starting from from
are replaced by patch
.
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.
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
.
Multiplies up the elements of this collection.
the product of all elements in this list 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 list 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.
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.
UnsupportedOperationException
if this traversable or iterator is empty.
Applies a binary operator to all elements of this sequence, going left to right.
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 left to right:
op( op( ... op(x_1, x_2) ..., x_{n-1}), x_n)
where x_{1}, ..., x_{n}
are the elements of this sequence.
UnsupportedOperationException
if this sequence is empty.
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)
if this traversable or iterator is nonempty, None
otherwise.
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.
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.
UnsupportedOperationException
if this sequence is empty.
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)
if this traversable or iterator is nonempty, None
otherwise.
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.
Returns new list with elements in reversed order.
A new list with all elements of this list 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
Builds a new collection by applying a function to all elements of this list and collecting the results in reversed order.
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 list resulting from applying the given function f
to each element of this list and collecting the results in reversed order.
Adds the elements of a given list in reverse order in front of this list. xs reverse_::: ys
is equivalent to xs.reverse ::: ys
but is more efficient.
the prefix to reverse and then prepend
the concatenation of the reversed prefix and the current list.
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
.
Checks if the other iterable collection contains the same elements in the same order as this list.
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.
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
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.
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 the new element type B
.
collection with intermediate results
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 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.
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., 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
.
Note: will not terminate for infinite-sized collections.
the number of elements in this sequence.
The size of this collection or iterator, if it can be cheaply computed
the number of elements in this collection or iterator, or -1 if the size cannot be determined cheaply
a list containing the elements greater than or equal to index from
extending up to (but not including) index until
of this list.
// Given a list val letters = List('a','b','c','d','e') // `slice` returns all elements beginning at index `from` and afterwards, // up until index `until` (excluding index `until`.) letters.slice(1,3) // Returns List('b','c')
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
An iterator producing iterable collections of size size
, except the last element (which may be the only element) will be truncated if there are fewer than size
elements remaining to be grouped.
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
.) The "sliding window" step is set to one.
the number of elements per group
An iterator producing iterable collections of size size
, except the last element (which may be the only element) will be truncated if there are fewer than size
elements remaining to be grouped.
scala.collection.Iterator, method sliding
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)
scala.math.Ordering Note: will not terminate for infinite-sized collections.
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.
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 list 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 list whose elements all satisfy p
, and the rest of this list.
Splits this list 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 lists consisting of the first n
elements of this list, and the other elements.
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.
the sequence to test
true
if this collection has that
as a prefix, false
otherwise.
Defines the prefix of this object's toString
representation.
a string representation which starts the result of toString
applied to this list. By default the string prefix is the simple name of the collection class list.
Sums up the elements of this collection.
the sum of all elements in this list 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 list and as result type of sum
. Examples of such types are: Long
, Float
, Double
, BigInt
.
Selects all elements except the first.
a list consisting of all elements of this list except the first one.
UnsupportedOperationException
if the list is empty.
Iterates over the tails of this sequence. The first value will be this sequence and the final one will be an empty sequence, with the intervening values the results of successive applications of tail
.
an iterator over all the tails of this sequence
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Selects first n elements.
the number of elements to take from this list.
a list consisting only of the first n
elements of this list, or else the whole list, if it has less than n
elements. If n
is negative, returns an empty list.
Selects last n elements.
the number of elements to take
a list consisting only of the last n
elements of this list, or else the whole list, if it has less than n
elements.
Takes longest prefix of elements that satisfy a predicate.
the longest prefix of this list whose elements all satisfy the predicate p
.
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
Converts this list into another by copying all elements.
The collection type to build.
a new collection containing all elements of this list.
Converts this list to an array.
an array containing all elements of this list. An ClassTag
must be available for the element type of this list.
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. By default this is implemented as just a cast, but this can be overridden. Seq
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.
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. 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 list to a list.
a list containing all elements of this list.
Converts this list 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.
a map of type immutable.Map[T, U]
containing all key/value pairs of type (T, U)
of this list.
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.
Note: will not terminate for infinite-sized collections.
a set containing all elements of this traversable or iterator.
Converts this list to a stream.
a stream containing all elements of this list.
Converts this sequence to a string.
a string representation of this collection. By default this string consists of the stringPrefix
of this sequence, followed by all elements separated by commas and enclosed in parentheses.
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.
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.
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.
IllegalArgumentException
if all collections in this collection are not of the same size.
Produces a new sequence which contains all elements of this list 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-preserving multi-set union of xs
and ys
. union
is hence a counter-part of diff
and intersect
which also work on multi-sets.
the sequence to add.
a new list which contains all elements of this list followed by all elements of that
.
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))
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.
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))
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.
A copy of this list with one single replaced element.
the position of the replacement
the replacing element
a copy of this list with the element at position index
replaced by elem
.
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 view of this sequence.
a non-strict view of this sequence.
Creates a non-strict filter of this traversable collection.
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.
Note: might return different results for different runs, unless the underlying collection type is ordered.
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 traversable collection which satisfy the predicate p
.
Returns a list formed from this list and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
a new list containing pairs consisting of corresponding elements of this list and that
. The length of the returned collection is the minimum of the lengths of this list and that
.
Returns a list formed from this list 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 list is shorter than that
.
the element to be used to fill up the result if that
is shorter than this list.
a new list containing pairs consisting of corresponding elements of this list and that
. The length of the returned collection is the maximum of the lengths of this list and that
. If this list is shorter than that
, thisElem
values are used to pad the result. If that
is shorter than this list, thatElem
values are used to pad the result.
Zips this list with its indices.
A new list containing pairs consisting of all elements of this list paired with their index. Indices start at 0
.
List("a", "b", "c").zipWithIndex = List(("a", 0), ("b", 1), ("c", 2))
(::: MonadOps[B]).filter(p)
(::: MonadOps[B]).flatMap(f)
(::: MonadOps[B]).map(f)
(::: MonadOps[B]).withFilter(p)
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala/collection/immutable/$colon$colon.html
A non empty list characterized by a head and a tail.
the type of the list elements.
the first element of the list
the list containing the remaining elements of this list after the first one.
2.8