Applies a binary operator to a start value and all elements of this collection 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 collection 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 x1, ..., xn
are the elements of this collection or iterator.
Applies a binary operator to all elements of this collection 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 collection 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 x1, ..., xn
are the elements of this collection or iterator.
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 collection 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
Counts the number of elements in the collection or iterator which satisfy a predicate.
the predicate used to test elements.
the number of elements satisfying the predicate p
.
Tests whether a predicate holds for at least one element of this collection or iterator.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
true
if the given predicate p
is satisfied by at least one element of this collection or iterator, otherwise false
Finds the first element of the collection or iterator 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.
the predicate used to test elements.
an option value containing the first element in the collection or iterator that satisfies p
, or None
if none exists.
Folds the elements of this collection 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 collection or iterator is empty.
Applies a binary operator to a start value and all elements of this collection 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 start value.
the binary operator.
the result of inserting op
between consecutive elements of this collection or iterator, going left to right with the start value z
on the left:
op(...op(z, x_1), x_2, ..., x_n)
where x1, ..., xn
are the elements of this collection or iterator. Returns z
if this collection or iterator is empty.
Applies a binary operator to all elements of this collection 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.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op
between consecutive elements of this collection 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 x1, ..., xn
are the elements of this collection or iterator. Returns z
if this collection or iterator is empty.
Tests whether a predicate holds for all elements of this collection or iterator.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
true
if this collection or iterator is empty or the given predicate p
holds for all elements of this collection or iterator, otherwise false
.
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
Tests whether this collection or iterator 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.
Tests whether the collection or iterator 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 collection or iterator contains no elements, false
otherwise.
Tests whether this collection or iterator can be repeatedly traversed. Always true for Traversables and false for Iterators unless overridden.
true
if it is repeatedly traversable, false
otherwise.
Displays all elements of this collection or iterator in a string.
a string representation of this collection or iterator. In the resulting string the string representations (w.r.t. the method toString
) of all elements of this collection or iterator follow each other without any separator string.
Displays all elements of this collection or iterator in a string using a separator string.
the separator string.
a string representation of this collection or iterator. In the resulting string the string representations (w.r.t. the method toString
) of all elements of this collection or iterator are separated by the string sep
.
List(1, 2, 3).mkString("|") = "1|2|3"
Displays all elements of this collection 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 collection 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 collection or iterator are separated by the string sep
.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Tests whether the collection or iterator is not empty.
true
if the collection or iterator contains at least one element, false
otherwise.
Reduces the elements of this collection 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 collection or iterator is nonempty.
UnsupportedOperationException
if this collection or iterator is empty.
Optionally applies a binary operator to all elements of this collection 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 collection or iterator is nonempty, None
otherwise.
Reduces the elements of this collection 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 collection 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.
the result of inserting op
between consecutive elements of this collection 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 collection or iterator.
UnsupportedOperationException
if this collection or iterator is empty.
Optionally applies a binary operator to all elements of this collection 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 collection or iterator is nonempty, None
otherwise.
The size of this collection or iterator.
Note: will not terminate for infinite-sized collections.
the number of elements in this collection or iterator.
Uses the contents of this collection or iterator to create a new mutable buffer.
Note: will not terminate for infinite-sized collections.
a buffer containing all elements of this collection or iterator.
Converts this collection or iterator to an indexed sequence.
Note: will not terminate for infinite-sized collections.
an indexed sequence containing all elements of this collection or iterator.
Converts this collection or iterator to an iterable collection. Note that the choice of target Iterable
is lazy in this default implementation as this TraversableOnce
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.
an Iterable
containing all elements of this collection or iterator.
Returns an Iterator over the elements in this collection or iterator. Will return the same Iterator if this instance is already an Iterator.
Note: will not terminate for infinite-sized collections.
an Iterator containing all elements of this collection or iterator.
Converts this collection or iterator to a list.
Note: will not terminate for infinite-sized collections.
a list containing all elements of this collection or iterator.
Converts this collection or iterator to a sequence. As with toIterable
, it's lazy in this default implementation, as this TraversableOnce
may be lazy and unevaluated.
Note: will not terminate for infinite-sized collections.
a sequence containing all elements of this collection or iterator.
Converts this collection or iterator to a set.
Note: will not terminate for infinite-sized collections.
a set containing all elements of this collection or iterator.
Converts this collection or iterator to a stream.
a stream containing all elements of this collection or iterator.
Converts this collection or iterator 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 collection or iterator.
Converts this collection or iterator to a Vector.
Note: will not terminate for infinite-sized collections.
a vector containing all elements of this collection or iterator.
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 ==
Test two objects for equality. 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.
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
.
Copies the elements of this collection or iterator to an array. Fills the given array xs
with at most len
elements of this collection or iterator, starting at position start
. Copying will stop once either the end of the current collection or iterator is reached, or the end of the target array is reached, or len
elements have been copied.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
the maximal number of elements to copy.
Copies the elements of this collection or iterator to an array. Fills the given array xs
with values of this collection or iterator, beginning at index start
. Copying will stop once either the end of the current collection or iterator is reached, or the end of the target array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
Copies the elements of this collection or iterator to an array. Fills the given array xs
with values of this collection or iterator. Copying will stop once either the end of the current collection or iterator is reached, or the end of the target array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
Compares the receiver object (this
) with the argument object (that
) for equivalence.
Any implementation of this method should be an equivalence relation:
x
of type Any
, x.equals(x)
should return true
.It is symmetric: for any instances x
and y
of type Any
, x.equals(y)
should return true
if and only if y.equals(x)
returns true
.It is transitive: for any instances x
, y
, and z
of type Any
if x.equals(y)
returns true
and y.equals(z)
returns true
, then x.equals(z)
should return true
. If you override this method, you should verify that your implementation remains an equivalence relation. Additionally, when overriding this method it is usually necessary to override hashCode
to ensure that objects which are "equal" (o1.equals(o2)
returns true
) hash to the same scala.Int. (o1.hashCode.equals(o2.hashCode)
).
true
if the receiver object is equivalent to the argument; false
otherwise.
Applies a function f
to all elements of this collection or iterator.
Note: this method underlies the implementation of most other bulk operations. It's important to implement this method in an efficient way.
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).
Calculate a hash code value for the object.
The default hashing algorithm is platform dependent.
Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)
) yet not be equal (o1.equals(o2)
returns false
). A degenerate implementation could always return 0
. However, it is required that if two objects are equal (o1.equals(o2)
returns true
) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)
). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals
method.
the hash code value for this object.
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.
Finds the largest element.
the largest element of this collection or iterator.
UnsupportedOperationException
if this collection or iterator 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 collection or iterator with the largest value measured by function f.
UnsupportedOperationException
if this collection or iterator is empty.
Finds the smallest element.
the smallest element of this collection or iterator
UnsupportedOperationException
if this collection or iterator 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 collection or iterator with the smallest value measured by function f.
UnsupportedOperationException
if this collection or iterator is empty.
Multiplies up the elements of this collection.
the product of all elements in this collection or iterator 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 collection or iterator and as result type of product
. Examples of such types are: Long
, Float
, Double
, BigInt
.
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
Sums up the elements of this collection.
the sum of all elements in this collection or iterator 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 collection or iterator and as result type of sum
. Examples of such types are: Long
, Float
, Double
, BigInt
.
Converts this collection or iterator into another by copying all elements.
Note: will not terminate for infinite-sized collections.
The collection type to build.
a new collection containing all elements of this collection or iterator.
Converts this collection or iterator to an array.
Note: will not terminate for infinite-sized collections.
an array containing all elements of this collection or iterator. An ClassTag
must be available for the element type of this collection or iterator.
Converts this collection or iterator to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.
Note: will not terminate for infinite-sized collections.
a map of type immutable.Map[T, U]
containing all key/value pairs of type (T, U)
of this collection or iterator.
Returns a string representation of the object.
The default representation is platform dependent.
a string representation of the object.
© 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/GenTraversableOnce.html
A template trait for all traversable-once objects which may be traversed in parallel.
Methods in this trait are either abstract or can be implemented in terms of other methods.