Scala Library
scala

class List
[source: scala/List.scala]
sealed abstract class List[+A]
extends Seq[A] with Product
A class representing an ordered collection of elements of type a. This class comes with two implementing case classes scala.Nil and scala.:: that implement the abstract members isEmpty, head and tail.
Author
Martin Odersky and others
Version
1.0, 16/07/2003
Direct Known Subclasses:
Nil, ::
Method Summary
def + [B >: A](x : B) : List[B]
override def ++ [B >: A](that : Iterable[B]) : List[B]
Appends two list objects.
def - [B >: A](x : B) : List[B]
Computes the difference between this list and the given object x.
def -- [B >: A](that : List[B]) : List[B]
Computes the difference between this list and the given list that.
def :: [B >: A](x : B) : List[B]
def ::: [B >: A](prefix : List[B]) : List[B]
def apply (n : Int) : A
Returns the n-th element of this list. The first element (head of the list) is at position 0.
def break (p : (A) => Boolean) : (List[A], List[A])
Like span but with the predicate inverted.
def count (p : (A) => Boolean) : Int
Count the number of elements in the list which satisfy a predicate.
def diff [B >: A](that : List[B]) : List[B]
Computes the difference between this list and the given list that.
override def drop (n : Int) : List[A]
Returns the list without its n first elements. If this list has less than n elements, the empty list is returned.
def dropRight (n : Int) : List[A]
Returns the list wihout its rightmost n elements.
override def dropWhile (p : (A) => Boolean) : List[A]
Returns the longest suffix of this list whose first element does not satisfy the predicate p.
override def elements : Iterator[A]
Returns the elements in the list as an iterator
override def exists (p : (A) => Boolean) : Boolean
Tests the existence in this list of an element that satisfies the predicate p.
override final def filter (p : (A) => Boolean) : List[A]
Returns all the elements of this list that satisfy the predicate p. The order of the elements is preserved. It is guarenteed that the receiver list itself is returned iff all its elements satisfy the predicate `p'. Hence the following equality is valid: (xs filter p) eq xs == xs forall p
override def find (p : (A) => Boolean) : Option[A]
Find and return the first element of the list satisfying a predicate, if any.
override final def flatMap [B](f : (A) => Iterable[B]) : List[B]
Applies the given function f to each element of this list, then concatenates the results.
def flatten [B](implicit f : (A) => Iterable[B]) : List[B]
Concatenate the elements of this list. The elements of this list should be a Iterables. Note: The compiler might not be able to infer the type parameter.
override def foldLeft [B](z : B)(f : (B, A) => B) : B
Combines the elements of this list together using the binary function f, from left to right, and starting with the value z.
override def foldRight [B](z : B)(f : (A, B) => B) : B
Combines the elements of this list together using the binary function f, from right to left, and starting with the value z.
override def forall (p : (A) => Boolean) : Boolean
Tests if the predicate p is satisfied by all elements in this list.
override final def foreach (f : (A) => Unit) : Unit
Apply the given function f to each element of this list (while respecting the order of the elements).
abstract def head : A
Returns this first element of the list.
def indices : List[Int]
Creates a list with all indices in the list. This is equivalent to a call to List.range(0, xs.length).
def init : List[A]
Returns the list without its last element.
def intersect [B >: A](that : List[B]) : List[B]
Computes the intersection between this list and the given list that.
override abstract def isEmpty : Boolean
Returns true if the list does not contain any elements.
override def last : A
Returns the last element of this list.
def length : Int
Returns the number of elements in the list.
override def lengthCompare (l : Int) : Int
Result of comparing length with operand l. returns x where x < 0 iff this.length < l x == 0 iff this.length == l x > 0 iff this.length > that. This method is used by matching streams against right-ignoring (...,_*) patterns. This method does not call List.length, it works for O(l), not for O(length).
override final def map [B](f : (A) => B) : List[B]
Returns the list resulting from applying the given function f to each element of this list.
override def partition (p : (A) => Boolean) : (List[A], List[A])
Partition the list in two sub-lists according to a predicate.
override def projection : Stream[A]
returns a projection that can be used to call non-strict filter, map, and flatMap methods that build projections of the collection.
override def reduceLeft [B >: A](f : (B, A) => B) : B
Combines the elements of this list together using the binary operator op, from left to right
override def reduceRight [B >: A](f : (A, B) => B) : B
Combines the elements of this list together using the binary operator op, from right to left
def remove (p : (A) => Boolean) : List[A]
Removes all elements of the list which satisfy the predicate p. This is like filter with the predicate inversed.
def removeDuplicates : List[A]
Removes redundant elements from the list. Uses the method == to decide if two elements are identical.
override def reverse : List[A]
A list consisting of all elements of this list in reverse order.
def reverseMap [B](f : (A) => B) : List[B]
Apply a function to all the elements of the list, and return the reversed list of results. This is equivalent to a call to map followed by a call to reverse, but more efficient.
def reverse_::: [B >: A](prefix : List[B]) : List[B]
Reverse the given prefix and append the current list to that. This function is equivalent to an application of reverse on the prefix followed by a call to :::, but more efficient (and tail recursive).
override def slice (start : Int, end : Int) : List[A]
Returns the list with elements belonging to the given index range.
def sort (lt : (A, A) => Boolean) : List[A]
def span (p : (A) => Boolean) : (List[A], List[A])
Returns the longest prefix of the list whose elements all satisfy the given predicate, and the rest of the list.
def splitAt (n : Int) : (List[A], List[A])
Split the list at a given point and return the two parts thus created.
protected override def stringPrefix : java.lang.String
Defines the prefix of this object's toString representation.
abstract def tail : List[A]
Returns this list without its first element.
override def take (n : Int) : List[A]
Returns the n first elements of this list, or else the whole list, if it has less than n elements.
def takeRight (n : Int) : List[A]
Returns the rightmost n elements from this list.
override def takeWhile (p : (A) => Boolean) : List[A]
Returns the longest prefix of this list whose elements satisfy the predicate p.
override def toList : List[A]
Overrides the method in Iterable for efficiency.
override def toStream : Stream[A]
Returns a stream containing all of the elements in this iterable object.
def union [B >: A](that : List[B]) : List[B]
Computes the union of this list and the given list that.
def zip [B](that : List[B]) : List[(A, B)]
Returns a list formed from this list and the specified list that by associating each element of the former with the element at the same position in the latter. If one of the two lists is longer than the other, its remaining elements are ignored.
def zipAll [B, C >: A, D >: B](that : List[B], thisElem : C, thatElem : D) : List[(C, D)]
Returns a list formed from this list and the specified list that by associating each element of the former with the element at the same position in the latter.
def zipWithIndex : List[(A, Int)]
Returns a list that pairs each element of this list with its index, counting from 0.
Methods inherited from Product
productElement (abstract), productArity (abstract), productPrefix
Methods inherited from Seq
size, concat, lastOption, first, firstOption, headOption, isDefinedAt, lastIndexOf, findIndexOf, indexOf, slice, contains, subseq, toArray, toSeq, equalsWith, startsWith, startsWith, endsWith, indexOf, containsSlice
Methods inherited from Collection
toString
Methods inherited from Iterable
/:, :\, copyToBuffer, sameElements, mkString, mkString, mkString, addString, addString, addString, copyToArray, hasDefiniteSize
Methods inherited from PartialFunction
orElse, andThen
Methods inherited from Function1
compose
Methods inherited from AnyRef
getClass, hashCode, equals, clone, notify, notifyAll, wait, wait, wait, finalize, ==, !=, eq, ne, synchronized
Methods inherited from Any
==, !=, isInstanceOf, asInstanceOf
Method Details
override abstract def isEmpty : Boolean
Returns true if the list does not contain any elements.
Returns
true, iff the list is empty.
Overrides
Seq.isEmpty
abstract def head : A
Returns this first element of the list.
Returns
the first element of this list.
Throws
Predef.NoSuchElementException - if the list is empty.
override def lengthCompare(l : Int) : Int
Result of comparing length with operand l. returns x where x < 0 iff this.length < l x == 0 iff this.length == l x > 0 iff this.length > that. This method is used by matching streams against right-ignoring (...,_*) patterns. This method does not call List.length, it works for O(l), not for O(length).
Overrides
Seq.lengthCompare
abstract def tail : List[A]
Returns this list without its first element.
Returns
this list without its first element.
Throws
Predef.NoSuchElementException - if the list is empty.
def ::[B >: A](x : B) : List[B]

Add an element x at the beginning of this list.

Parameters
x - the element to prepend.
Returns
the list with x added at the beginning.
Examples
1 :: List(2, 3) = List(2, 3).::(1) = List(1, 2, 3)
@deprecated

def +[B >: A](x : B) : List[B]

Add an element x at the end of this list.

Deprecated
Replace uses of l + e with l ::: List(e).
Parameters
x - the element to append.
Returns
the list with x added at the end.
def :::[B >: A](prefix : List[B]) : List[B]

Returns a list resulting from the concatenation of the given list prefix and this list.

Parameters
prefix - the list to concatenate at the beginning of this list.
Returns
the concatenation of the two lists.
Examples
List(1, 2) ::: List(3, 4) = List(3, 4).:::(List(1, 2)) = List(1, 2, 3, 4)
override def ++[B >: A](that : Iterable[B]) : List[B]
Appends two list objects.
Overrides
Seq.++
def reverse_:::[B >: A](prefix : List[B]) : List[B]
Reverse the given prefix and append the current list to that. This function is equivalent to an application of reverse on the prefix followed by a call to :::, but more efficient (and tail recursive).
Parameters
prefix - the prefix to reverse and then prepend
Returns
the concatenation of the reversed prefix and the current list.
def length : Int
Returns the number of elements in the list.
Returns
the number of elements in the list.
Overrides
Seq.length
def indices : List[Int]
Creates a list with all indices in the list. This is equivalent to a call to List.range(0, xs.length).
Returns
a list of all indices in the list.
override def elements : Iterator[A]
Returns the elements in the list as an iterator
Returns
an iterator on the list elements.
override def toList : List[A]
Overrides the method in Iterable for efficiency.
Returns
the list itself
def init : List[A]
Returns the list without its last element.
Returns
the list without its last element.
Throws
Predef.UnsupportedOperationException - if the list is empty.
override def last : A
Returns the last element of this list.
Returns
the last element of the list.
Throws
Predef.NoSuchElementException - if the list is empty.
Overrides
Seq.last
override def take(n : Int) : List[A]
Returns the n first elements of this list, or else the whole list, if it has less than n elements.
Parameters
n - the number of elements to take.
Returns
the n first elements of this list.
Overrides
Seq.take
override def slice(start : Int, end : Int) : List[A]
Returns the list with elements belonging to the given index range.
Parameters
start - the start position of the list slice.
end - the end position (exclusive) of the list slice.
Returns
the list with elements belonging to the given index range.
Overrides
Seq.slice
override def drop(n : Int) : List[A]
Returns the list without its n first elements. If this list has less than n elements, the empty list is returned.
Parameters
n - the number of elements to drop.
Returns
the list without its n first elements.
Overrides
Seq.drop
def takeRight(n : Int) : List[A]
Returns the rightmost n elements from this list.
Parameters
n - the number of elements to take
Returns
the suffix of length n of the list
def dropRight(n : Int) : List[A]
Returns the list wihout its rightmost n elements.
Parameters
n - the number of elements to take
Returns
the suffix of length n of the list
def splitAt(n : Int) : (List[A], List[A])
Split the list at a given point and return the two parts thus created.
Parameters
n - the position at which to split
Returns
a pair of lists composed of the first n elements, and the other elements.
override def takeWhile(p : (A) => Boolean) : List[A]
Returns the longest prefix of this list whose elements satisfy the predicate p.
Parameters
p - the test predicate.
Returns
the longest prefix of this list whose elements satisfy the predicate p.
Overrides
Seq.takeWhile
override def dropWhile(p : (A) => Boolean) : List[A]
Returns the longest suffix of this list whose first element does not satisfy the predicate p.
Parameters
p - the test predicate.
Returns
the longest suffix of the list whose first element does not satisfy the predicate p.
Overrides
Seq.dropWhile
def span(p : (A) => Boolean) : (List[A], List[A])
Returns the longest prefix of the list whose elements all satisfy the given predicate, and the rest of the list.
Parameters
p - the test predicate
Returns
a pair consisting of the longest prefix of the list whose elements all satisfy p, and the rest of the list.
def break(p : (A) => Boolean) : (List[A], List[A])
Like span but with the predicate inverted.
def apply(n : Int) : A
Returns the n-th element of this list. The first element (head of the list) is at position 0.
Parameters
n - index of the element to return
Returns
the element at position n in this list.
Throws
Predef.NoSuchElementException - if the list is too short.
override final def map[B](f : (A) => B) : List[B]
Returns the list resulting from applying the given function f to each element of this list.
Parameters
f - function to apply to each element.
Returns
[f(a0), ..., f(an)] if this list is [a0, ..., an].
Overrides
Seq.map
def reverseMap[B](f : (A) => B) : List[B]
Apply a function to all the elements of the list, and return the reversed list of results. This is equivalent to a call to map followed by a call to reverse, but more efficient.
Parameters
f - the function to apply to each elements.
Returns
the reversed list of results.
override final def foreach(f : (A) => Unit) : Unit
Apply the given function f to each element of this list (while respecting the order of the elements).
Parameters
f - the treatment to apply to each element.
override final def filter(p : (A) => Boolean) : List[A]
Returns all the elements of this list that satisfy the predicate p. The order of the elements is preserved. It is guarenteed that the receiver list itself is returned iff all its elements satisfy the predicate `p'. Hence the following equality is valid: (xs filter p) eq xs == xs forall p
Parameters
p - the predicate used to filter the list.
Returns
the elements of this list satisfying p.
Overrides
Seq.filter
def remove(p : (A) => Boolean) : List[A]
Removes all elements of the list which satisfy the predicate p. This is like filter with the predicate inversed.
Parameters
p - the predicate to use to test elements
Returns
the list without all elements which satisfy p
override def partition(p : (A) => Boolean) : (List[A], List[A])
Partition the list in two sub-lists according to a predicate.
Parameters
p - the predicate on which to partition
Returns
a pair of lists: the list of all elements which satisfy p and the list of all elements which do not. The relative order of the elements in the sub-lists is the same as in the original list.
def sort(lt : (A, A) => Boolean) : List[A]

Sort the list according to the comparison function <(e1: a, e2: a) => Boolean, which should be true iff e1 is smaller than e2.

Parameters
lt - the comparison function
Returns
a list sorted according to the comparison function <(e1: a, e2: a) => Boolean.
Examples
      List("Steve", "Tom", "John", "Bob")
        .sort((e1, e2) => (e1 compareTo e2) < 0) =
      List("Bob", "John", "Steve", "Tom")
def count(p : (A) => Boolean) : Int
Count the number of elements in the list which satisfy a predicate.
Parameters
p - the predicate for which to count
Returns
the number of elements satisfying the predicate p.
override def forall(p : (A) => Boolean) : Boolean
Tests if the predicate p is satisfied by all elements in this list.
Parameters
p - the test predicate.
Returns
true iff all elements of this list satisfy the predicate p.
override def exists(p : (A) => Boolean) : Boolean
Tests the existence in this list of an element that satisfies the predicate p.
Parameters
p - the test predicate.
Returns
true iff there exists an element in this list that satisfies the predicate p.
override def find(p : (A) => Boolean) : Option[A]
Find and return the first element of the list satisfying a predicate, if any.
Parameters
p - the predicate
Returns
the first element in the list satisfying p, or None if none exists.
override def foldLeft[B](z : B)(f : (B, A) => B) : B
Combines the elements of this list together using the binary function f, from left to right, and starting with the value z.
Returns
f(... (f(f(z, a0), a1) ...), an) if the list is [a0, a1, ..., an].
override def foldRight[B](z : B)(f : (A, B) => B) : B
Combines the elements of this list together using the binary function f, from right to left, and starting with the value z.
Returns
f(a0, f(a1, f(..., f(an, z)...))) if the list is [a0, a1, ..., an].
override def reduceLeft[B >: A](f : (B, A) => B) : B
Combines the elements of this list together using the binary operator op, from left to right
Parameters
op - The operator to apply
Returns
op(... op(a0,a1), ..., an) if the list has elements a0, a1, ..., an.
Throws
Predef.UnsupportedOperationException - if the list is empty.
override def reduceRight[B >: A](f : (A, B) => B) : B
Combines the elements of this list together using the binary operator op, from right to left
Parameters
op - The operator to apply
Returns
a0 op (... op (an-1 op an)...) if the list has elements a0, a1, ..., an.
Throws
Predef.UnsupportedOperationException - if the list is empty.
override final def flatMap[B](f : (A) => Iterable[B]) : List[B]
Applies the given function f to each element of this list, then concatenates the results.
Parameters
f - the function to apply on each element.
Returns
f(a0) ::: ... ::: f(an) if this list is [a0, ..., an].
Overrides
Seq.flatMap
override def reverse : List[A]
A list consisting of all elements of this list in reverse order.
Overrides
Seq.reverse
def zip[B](that : List[B]) : List[(A, B)]
Returns a list formed from this list and the specified list that by associating each element of the former with the element at the same position in the latter. If one of the two lists is longer than the other, its remaining elements are ignored.
Returns
List((a0,b0), ..., (amin(m,n),bmin(m,n))) when List(a0, ..., am) zip List(b0, ..., bn) is invoked.
def zipWithIndex : List[(A, Int)]
Returns a list that pairs each element of this list with its index, counting from 0.
Returns
the list List((a0,0), (a1,1), ...) where ai are the elements of this list.
def zipAll[B, C >: A, D >: B](that : List[B], thisElem : C, thatElem : D) : List[(C, D)]
Returns a list formed from this list and the specified list that by associating each element of the former with the element at the same position in the latter.
Parameters
that - list that may have a different length as the self list.
thisElem - element thisElem is used to fill up the resulting list if the self list is shorter than that
thatElem - element thatElem is used to fill up the resulting list if that is shorter than the self list
Returns
List((a0,b0), ..., (an,bn), (elem,bn+1), ..., {elem,bm}) when [a0, ..., an] zip [b0, ..., bm] is invoked where m > n.
def union[B >: A](that : List[B]) : List[B]
Computes the union of this list and the given list that.
Parameters
that - the list of elements to add to the list.
Returns
a list without doubles containing the elements of this list and those of the given list that.
@deprecated

def diff[B >: A](that : List[B]) : List[B]
Computes the difference between this list and the given list that.
Parameters
that - the list of elements to remove from this list.
Returns
this list without the elements of the given list that.
Deprecated
use -- instead
def --[B >: A](that : List[B]) : List[B]
Computes the difference between this list and the given list that.
Parameters
that - the list of elements to remove from this list.
Returns
this list without the elements of the given list that.
def -[B >: A](x : B) : List[B]
Computes the difference between this list and the given object x.
Parameters
x - the object to remove from this list.
Returns
this list without the elements of the given object x.
def flatten[B](implicit f : (A) => Iterable[B]) : List[B]
Concatenate the elements of this list. The elements of this list should be a Iterables. Note: The compiler might not be able to infer the type parameter.
Parameters
f - An implicit conversion to an Iterable instance.
Returns
The concatenation of all elements of iterables in this list.
def intersect[B >: A](that : List[B]) : List[B]
Computes the intersection between this list and the given list that.
Parameters
that - the list to intersect.
Returns
the list of elements contained both in this list and in the given list that.
def removeDuplicates : List[A]
Removes redundant elements from the list. Uses the method == to decide if two elements are identical.
Returns
the list without doubles.
protected override def stringPrefix : java.lang.String
Defines the prefix of this object's toString representation.
override def projection : Stream[A]
returns a projection that can be used to call non-strict filter, map, and flatMap methods that build projections of the collection.
Overrides
Seq.projection
override def toStream : Stream[A]
Returns a stream containing all of the elements in this iterable object.
Notes
consider using projection for lazy behavior.
Scala Library