Represents optional values. Instances of Option
are either an instance of scala.Some or the object None
.
The most idiomatic way to use an scala.Option instance is to treat it
as a collection or monad and use map
,flatMap
, filter
, or
foreach
:
val name: Option[String] = request getParameter "name"
val upper = name map { _.trim } filter { _.length != 0 } map { _.toUpperCase }
println(upper getOrElse "")
Note that this is equivalent to
val upper = for {
name <- request getParameter "name"
trimmed <- Some(name.trim)
upper <- Some(trimmed.toUpperCase) if trimmed.length != 0
} yield upper
println(upper getOrElse "")
Because of how for comprehension works, if None
is returned
from request.getParameter
, the entire expression results in
None
This allows for sophisticated chaining of scala.Option values without having to check for the existence of a value.
These are useful methods that exist for both scala.Some and None
.
- isDefined — True if not empty
- isEmpty — True if empty
- nonEmpty — True if not empty
- orElse — Evaluate and return alternate optional value if empty
- getOrElse — Evaluate and return alternate value if empty
- get — Return value, throw exception if empty
- fold — Apply function on optional value, return default if empty
- map — Apply a function on the optional value
- flatMap — Same as map but function must return an optional value
- foreach — Apply a procedure on option value
- collect — Apply partial pattern match on optional value
- filter — An optional value satisfies predicate
- filterNot — An optional value doesn't satisfy predicate
- exists — Apply predicate on optional value, or false if empty
- forall — Apply predicate on optional value, or true if empty
- contains — Checks if value equals optional value, or false if empty
- zip — Combine two optional values to make a paired optional value
- unzip — Split an optional pair to two optional values
- unzip3 — Split an optional triple to three optional values
- toList — Unary list of optional value, otherwise the empty list
A less-idiomatic way to use scala.Option values is via pattern matching:
val nameMaybe = request getParameter "name"
nameMaybe match {
case Some(name) =>
println(name.trim.toUppercase)
case None =>
println("No name value")
}
Interacting with code that can occasionally return null can be
safely wrapped in scala.Option to become None
and scala.Some otherwise.
val abc = new java.util.HashMap[Int, String]
abc.put(1, "A")
bMaybe = Option(abc.get(2))
bMaybe match {
case Some(b) =>
println(s"Found $b")
case None =>
println("Not found")
}
- Note:
Many of the methods in here are duplicative with those in the Traversable hierarchy, but they are duplicated for a reason: the implicit conversion tends to leave one with an Iterable in situations where one could have retained an Option.
- Companion:
- object
- Source:
- Option.scala
Type members
Classlikes
We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.
We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.
- Source:
- Option.scala
Value members
Abstract methods
Returns the option's value.
Returns the option's value.
This is equivalent to:
option match {
case Some(x) => x
case None => throw new Exception
}
- Throws:
- NoSuchElementException
if the option is empty.
- Note:
The option must be nonempty.
- Source:
- Option.scala
Concrete methods
Returns a scala.Some containing the result of
applying pf
to this scala.Option's contained
value, if this option is
nonempty and pf
is defined for that value.
Returns a scala.Some containing the result of
applying pf
to this scala.Option's contained
value, if this option is
nonempty and pf
is defined for that value.
Returns None
otherwise.
- Value parameters:
- pf
the partial function.
- Returns:
the result of applying
pf
to this scala.Option's value (if possible), orNone
.- Example:
// Returns Some(HTTP) because the partial function covers the case. Some("http") collect {case "http" => "HTTP"} // Returns None because the partial function doesn't cover the case. Some("ftp") collect {case "http" => "HTTP"} // Returns None because the option is empty. There is no value to pass to the partial function. None collect {case value => value}
- Source:
- Option.scala
Tests whether the option contains a given value as an element.
Tests whether the option contains a given value as an element.
This is equivalent to:
option match {
case Some(x) => x == elem
case None => false
}
- Value parameters:
- elem
the element to test.
- Returns:
true
if the option has an element that is equal (as determined by==
) toelem
,false
otherwise.- Example:
// Returns true because Some instance contains string "something" which equals "something". Some("something") contains "something" // Returns false because "something" != "anything". Some("something") contains "anything" // Returns false when method called on None. None contains "anything"
- Source:
- Option.scala
Returns true if this option is nonempty and the predicate
p
returns true when applied to this scala.Option's value.
Returns true if this option is nonempty and the predicate
p
returns true when applied to this scala.Option's value.
Otherwise, returns false.
This is equivalent to:
option match {
case Some(x) => p(x)
case None => false
}
- Value parameters:
- p
the predicate to test
- Source:
- Option.scala
Returns this scala.Option if it is nonempty and applying the predicate p
to
this scala.Option's value returns true.
Returns this scala.Option if it is nonempty and applying the predicate p
to
this scala.Option's value returns true. Otherwise, return None
.
This is equivalent to:
option match {
case Some(x) if p(x) => Some(x)
case _ => None
}
- Value parameters:
- p
the predicate used for testing.
- Source:
- Option.scala
Returns this scala.Option if it is nonempty and applying the predicate p
to
this scala.Option's value returns false.
Returns this scala.Option if it is nonempty and applying the predicate p
to
this scala.Option's value returns false. Otherwise, return None
.
This is equivalent to:
option match {
case Some(x) if !p(x) => Some(x)
case _ => None
}
- Value parameters:
- p
the predicate used for testing.
- Source:
- Option.scala
Returns the result of applying f
to this scala.Option's value if
this scala.Option is nonempty.
Returns the result of applying f
to this scala.Option's value if
this scala.Option is nonempty.
Returns None
if this scala.Option is empty.
Slightly different from map
in that f
is expected to
return an scala.Option (which could be None
).
This is equivalent to:
option match {
case Some(x) => f(x)
case None => None
}
- Value parameters:
- f
the function to apply
- See also:
map
foreach
- Source:
- Option.scala
Returns the nested scala.Option value if it is nonempty.
Returns the nested scala.Option value if it is nonempty. Otherwise,
return None
.
This is equivalent to:
option match {
case Some(Some(b)) => Some(b)
case _ => None
}
- Value parameters:
- ev
an implicit conversion that asserts that the value is also an scala.Option.
- See also:
flatMap
- Example:
Some(Some("something")).flatten
- Source:
- Option.scala
Returns the result of applying f
to this scala.Option's
value if the scala.Option is nonempty.
Returns the result of applying f
to this scala.Option's
value if the scala.Option is nonempty. Otherwise, evaluates
expression ifEmpty
.
This is equivalent to:
option match {
case Some(x) => f(x)
case None => ifEmpty
}
This is also equivalent to:
option map f getOrElse ifEmpty
- Value parameters:
- f
the function to apply if nonempty.
- ifEmpty
the expression to evaluate if empty.
- Source:
- Option.scala
Returns true if this option is empty or the predicate
p
returns true when applied to this scala.Option's value.
Returns true if this option is empty or the predicate
p
returns true when applied to this scala.Option's value.
This is equivalent to:
option match {
case Some(x) => p(x)
case None => true
}
- Value parameters:
- p
the predicate to test
- Source:
- Option.scala
Apply the given procedure f
to the option's value,
if it is nonempty.
Apply the given procedure f
to the option's value,
if it is nonempty. Otherwise, do nothing.
This is equivalent to:
option match {
case Some(x) => f(x)
case None => ()
}
- Value parameters:
- f
the procedure to apply.
- See also:
map
flatMap
- Source:
- Option.scala
Returns the option's value if the option is nonempty, otherwise
return the result of evaluating default
.
Returns the option's value if the option is nonempty, otherwise
return the result of evaluating default
.
This is equivalent to:
option match {
case Some(x) => x
case None => default
}
- Value parameters:
- default
the default expression.
- Source:
- Option.scala
Returns true if the option is an instance of scala.Some, false otherwise.
Returns true if the option is an instance of scala.Some, false otherwise.
This is equivalent to:
option match {
case Some(_) => true
case None => false
}
- Source:
- Option.scala
Returns true if the option is None
, false otherwise.
Returns true if the option is None
, false otherwise.
This is equivalent to:
option match {
case Some(_) => false
case None => true
}
- Source:
- Option.scala
Returns a singleton iterator returning the scala.Option's value if it is nonempty, or an empty iterator if the option is empty.
Returns a singleton iterator returning the scala.Option's value if it is nonempty, or an empty iterator if the option is empty.
- Source:
- Option.scala
Analogous to zip
except that the elements in each collection are not consumed until a strict operation is
invoked on the returned LazyZip2
decorator.
Analogous to zip
except that the elements in each collection are not consumed until a strict operation is
invoked on the returned LazyZip2
decorator.
Calls to lazyZip
can be chained to support higher arities (up to 4) without incurring the expense of
constructing and deconstructing intermediary tuples.
val xs = List(1, 2, 3)
val res = (xs lazyZip xs lazyZip xs lazyZip xs).map((a, b, c, d) => a + b + c + d)
// res == List(4, 8, 12)
- Type parameters:
- B
the type of the second element in each eventual pair
- Value parameters:
- that
the iterable providing the second element of each eventual pair
- Returns:
a decorator
LazyZip2
that allows strict operations to be performed on the lazily evaluated pairs or chained calls tolazyZip
. Implicit conversion toIterable[(A, B)]
is also supported.- Source:
- Iterable.scala
Returns a scala.Some containing the result of applying f
to this scala.Option's
value if this scala.Option is nonempty.
Returns a scala.Some containing the result of applying f
to this scala.Option's
value if this scala.Option is nonempty.
Otherwise return None
.
This is equivalent to:
option match {
case Some(x) => Some(f(x))
case None => None
}
- Value parameters:
- f
the function to apply
- See also:
flatMap
foreach
- Note:
This is similar to
flatMap
except here,f
does not need to wrap its result in an scala.Option.- Source:
- Option.scala
Returns false if the option is None
, true otherwise.
Returns false if the option is None
, true otherwise.
This is equivalent to:
option match {
case Some(_) => true
case None => false
}
- Note:
Implemented here to avoid the implicit conversion to Iterable.
- Source:
- Option.scala
Returns this scala.Option if it is nonempty,
otherwise return the result of evaluating alternative
.
Returns this scala.Option if it is nonempty,
otherwise return the result of evaluating alternative
.
This is equivalent to:
option match {
case Some(x) => Some(x)
case None => alternative
}
- Value parameters:
- alternative
the alternative expression.
- Source:
- Option.scala
Returns the option's value if it is nonempty,
or null
if it is empty.
Returns the option's value if it is nonempty,
or null
if it is empty.
Although the use of null is discouraged, code written to use scala.Option must often interface with code that expects and returns nulls.
This is equivalent to:
option match {
case Some(x) => x
case None => null
}
- Example:
val initialText: Option[String] = getInitialText val textField = new JComponent(initialText.orNull,20)
- Source:
- Option.scala
Returns a scala.util.Right containing the given
argument right
if this is empty, or
a scala.util.Left containing this scala.Option's value
if this scala.Option is nonempty.
Returns a scala.util.Right containing the given
argument right
if this is empty, or
a scala.util.Left containing this scala.Option's value
if this scala.Option is nonempty.
This is equivalent to:
option match {
case Some(x) => Left(x)
case None => Right(right)
}
- Value parameters:
- right
the expression to evaluate and return if this is empty
- See also:
toRight
- Source:
- Option.scala
Returns a singleton list containing the scala.Option's value if it is nonempty, or the empty list if the scala.Option is empty.
Returns a singleton list containing the scala.Option's value if it is nonempty, or the empty list if the scala.Option is empty.
This is equivalent to:
option match {
case Some(x) => List(x)
case None => Nil
}
- Source:
- Option.scala
Returns a scala.util.Left containing the given
argument left
if this scala.Option is empty, or
a scala.util.Right containing this scala.Option's value if
this is nonempty.
Returns a scala.util.Left containing the given
argument left
if this scala.Option is empty, or
a scala.util.Right containing this scala.Option's value if
this is nonempty.
This is equivalent to:
option match {
case Some(x) => Right(x)
case None => Left(left)
}
- Value parameters:
- left
the expression to evaluate and return if this is empty
- See also:
toLeft
- Source:
- Option.scala
Converts an Option of a pair into an Option of the first element and an Option of the second element.
Converts an Option of a pair into an Option of the first element and an Option of the second element.
This is equivalent to:
option match {
case Some((x, y)) => (Some(x), Some(y))
case _ => (None, None)
}
- Type parameters:
- A1
the type of the first half of the element pair
- A2
the type of the second half of the element pair
- Value parameters:
- asPair
an implicit conversion which asserts that the element type of this Option is a pair.
- Returns:
a pair of Options, containing, respectively, the first and second half of the element pair of this Option.
- Source:
- Option.scala
Converts an Option of a triple into three Options, one containing the element from each position of the triple.
Converts an Option of a triple into three Options, one containing the element from each position of the triple.
This is equivalent to:
option match {
case Some((x, y, z)) => (Some(x), Some(y), Some(z))
case _ => (None, None, None)
}
- Type parameters:
- A1
the type of the first of three elements in the triple
- A2
the type of the second of three elements in the triple
- A3
the type of the third of three elements in the triple
- Value parameters:
- asTriple
an implicit conversion which asserts that the element type of this Option is a triple.
- Returns:
a triple of Options, containing, respectively, the first, second, and third elements from the element triple of this Option.
- Source:
- Option.scala
Necessary to keep scala.Option from being implicitly converted to
scala.collection.Iterable in for
comprehensions.
Necessary to keep scala.Option from being implicitly converted to
scala.collection.Iterable in for
comprehensions.
- Source:
- Option.scala
Returns a scala.Some formed from this option and another option by combining the corresponding elements in a pair.
Returns a scala.Some formed from this option and another option
by combining the corresponding elements in a pair.
If either of the two options is empty, None
is returned.
This is equivalent to:
(option1, option2) match {
case (Some(x), Some(y)) => Some((x, y))
case _ => None
}
- Value parameters:
- that
the options which is going to be zipped
- Example:
// Returns Some(("foo", "bar")) because both options are nonempty. Some("foo") zip Some("bar") // Returns None because `that` option is empty. Some("foo") zip None // Returns None because `this` option is empty. None zip Some("bar")
- Source:
- Option.scala
Deprecated methods
- Deprecated
- Source:
- Iterable.scala
- Deprecated
- Source:
- Iterable.scala
Inherited methods
Alias for concat
Alias for concat
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Appends all elements of this collection to a string builder.
Appends all elements of this collection to a string builder.
The written text consists of the string representations (w.r.t. the method
toString
) of all elements of this collection 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
- Value parameters:
- b
the string builder to which elements are appended.
- Returns:
the string builder
b
to which elements were appended.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Appends all elements of this collection to a string builder using a separator string.
Appends all elements of this collection 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 collection, 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
- Value parameters:
- b
the string builder to which elements are appended.
- sep
the separator string.
- Returns:
the string builder
b
to which elements were appended.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Appends all elements of this collection to a string builder using start, end, and separator strings.
Appends all elements of this collection 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 collection 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)
- Value parameters:
- b
the string builder to which elements are appended.
- end
the ending string.
- sep
the separator string.
- start
the starting string.
- Returns:
the string builder
b
to which elements were appended.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
A method that should be called from every well-designed equals method that is open to be overridden in a subclass.
A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.
- Value parameters:
- that
the value being probed for possible equality
- Returns:
true if this instance can possibly equal
that
, otherwise false- Inherited from:
- Equals
- Source:
- Equals.scala
Finds the first element of the collection for which the given partial function is defined, and applies the partial function to it.
Finds the first element of the collection 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.
- Value parameters:
- pf
the partial function
- Returns:
an option value containing pf applied to the first value for which it is defined, or
None
if none exists.- Example:
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Returns a new iterable collection containing the elements from the left hand operand followed by the elements from the right hand operand.
Returns a new iterable collection containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the iterable collection is the most specific superclass encompassing the element types of the two operands.
- Type parameters:
- B
the element type of the returned collection.
- Value parameters:
- suffix
the traversable to append.
- Returns:
a new iterable collection which contains all elements of this iterable collection followed by all elements of
suffix
.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Copy elements to an array, returning the number of elements written.
Copy elements to an array, returning the number of elements written.
Fills the given array xs
starting at index start
with at most len
elements of this collection.
Copying will stop once either all the elements of this collection have been copied,
or the end of the array is reached, or len
elements have been copied.
- Type parameters:
- B
the type of the elements of the array.
- Value parameters:
- len
the maximal number of elements to copy.
- start
the starting index of xs.
- xs
the array to fill.
- Returns:
the number of elements written to the array
- Note:
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Copy elements to an array, returning the number of elements written.
Copy elements to an array, returning the number of elements written.
Fills the given array xs
starting at index start
with values of this collection.
Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.
- Type parameters:
- B
the type of the elements of the array.
- Value parameters:
- start
the starting index of xs.
- xs
the array to fill.
- Returns:
the number of elements written to the array
- Note:
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Copy elements to an array, returning the number of elements written.
Copy elements to an array, returning the number of elements written.
Fills the given array xs
starting at index start
with values of this collection.
Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.
- Type parameters:
- B
the type of the elements of the array.
- Value parameters:
- xs
the array to fill.
- Returns:
the number of elements written to the array
- Note:
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.
Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
the type of the elements of
that
- Value parameters:
- p
the test predicate, which relates elements from both collections
- that
the other collection
- Returns:
true
if both collections have the same length andp(x, y)
istrue
for all corresponding elementsx
of this iterator andy
ofthat
, otherwisefalse
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Counts the number of elements in the collection which satisfy a predicate.
Counts the number of elements in the collection which satisfy a predicate.
Note: will not terminate for infinite-sized collections.
- Value parameters:
- p
the predicate used to test elements.
- Returns:
the number of elements satisfying the predicate
p
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Selects all elements except last n ones.
Selects all elements except last n ones.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Value parameters:
- n
the number of elements to drop from this iterable collection.
- Returns:
a iterable collection consisting of all elements of this iterable collection except the last
n
ones, or else the empty iterable collection, if this iterable collection has less thann
elements. Ifn
is negative, don't drop any elements.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Tests whether a predicate holds for at least one element of this collection.
Tests whether a predicate holds for at least one element of this collection.
Note: may not terminate for infinite-sized collections.
- Value parameters:
- p
the predicate used to test elements.
- Returns:
true
if the given predicatep
is satisfied by at least one element of this collection, otherwisefalse
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element of the collection satisfying a predicate, if any.
Finds the first element of the collection satisfying a predicate, if any.
Note: may not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Value parameters:
- p
the predicate used to test elements.
- Returns:
an option value containing the first element in the collection that satisfies
p
, orNone
if none exists.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Folds the elements of this collection using the specified associative binary operator.
Folds the elements of this collection using the specified associative binary operator.
The default implementation in IterableOnce
is equivalent to foldLeft
but may be
overridden for more efficient traversal orders.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- A1
a type parameter for the binary operator, a supertype of
A
.
- Value parameters:
- op
a binary operator that must be associative.
- z
a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g.,
Nil
for list concatenation, 0 for addition, or 1 for multiplication).
- Returns:
the result of applying the fold operator
op
between all the elements andz
, orz
if this collection is empty.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Applies a binary operator to a start value and all elements of this collection, going left to right.
Applies a binary operator to a start value and all elements of this collection, 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- z
the start value.
- Returns:
the result of inserting
op
between consecutive elements of this collection, going left to right with the start valuez
on the left:op(...op(z, x1), x2, ..., xn)
wherex1, ..., xn
are the elements of this collection. Returnsz
if this collection is empty.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Applies a binary operator to all elements of this collection and a start value, going right to left.
Applies a binary operator to all elements of this collection 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- z
the start value.
- Returns:
the result of inserting
op
between consecutive elements of this collection, going right to left with the start valuez
on the right:op(x1, op(x2, ... op(xn, z)...))
wherex1, ..., xn
are the elements of this collection. Returnsz
if this collection is empty.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether a predicate holds for all elements of this collection.
Tests whether a predicate holds for all elements of this collection.
Note: may not terminate for infinite-sized collections.
- Value parameters:
- p
the predicate used to test elements.
- Returns:
true
if this collection is empty or the given predicatep
holds for all elements of this collection, otherwisefalse
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Apply f
to each element for its side effects
Note: [U] parameter needed to help scalac's type inference.
Apply f
to each element for its side effects
Note: [U] parameter needed to help scalac's type inference.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Partitions this iterable collection into a map of iterable collections according to some discriminator function.
Partitions this iterable collection into a map of iterable collections according to some discriminator function.
Note: Even when applied to a view or a lazy collection it will always force the elements.
- Type parameters:
- K
the type of keys returned by the discriminator function.
- Value parameters:
- f
the discriminator function.
- Returns:
A map from keys to iterable 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 iterable collection of those elementsx
for whichf(x)
equalsk
.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Partitions this iterable collection into a map of iterable collections according to a discriminator function key
.
Partitions this iterable collection into a map of iterable collections according to a discriminator function key
.
Each element in a group is transformed into a value of type B
using the value
function.
It is equivalent to groupBy(key).mapValues(_.map(f))
, but more efficient.
case class User(name: String, age: Int)
def namesByAge(users: Seq[User]): Map[Int, Seq[String]] =
users.groupMap(_.age)(_.name)
Note: Even when applied to a view or a lazy collection it will always force the elements.
- Type parameters:
- B
the type of values returned by the transformation function
- K
the type of keys returned by the discriminator function
- Value parameters:
- f
the element transformation function
- key
the discriminator function
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Partitions this iterable collection into a map according to a discriminator function key
.
Partitions this iterable collection into a map according to a discriminator function key
. All the values that
have the same discriminator are then transformed by the f
function and then reduced into a
single value with the reduce
function.
It is equivalent to groupBy(key).mapValues(_.map(f).reduce(reduce))
, but more efficient.
def occurrences[A](as: Seq[A]): Map[A, Int] =
as.groupMapReduce(identity)(_ => 1)(_ + _)
Note: Even when applied to a view or a lazy collection it will always force the elements.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Partitions elements in fixed size iterable collections.
Partitions elements in fixed size iterable collections.
- Value parameters:
- size
the number of elements per group
- Returns:
An iterator producing iterable collections of size
size
, except the last will be less than sizesize
if the elements don't divide evenly.- See also:
scala.collection.Iterator, method
grouped
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Selects the first element of this iterable collection.
Selects the first element of this iterable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Returns:
the first element of this iterable collection.
- Throws:
- NoSuchElementException
if the iterable collection is empty.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Optionally selects the first element.
Optionally selects the first element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Returns:
the first element of this iterable collection if it is nonempty,
None
if it is empty.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
The initial part of the collection without its last element.
The initial part of the collection without its last element.
Note: Even when applied to a view or a lazy collection it will always force the elements.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Iterates over the inits of this iterable collection.
Iterates over the inits of this iterable collection. The first value will be this
iterable collection and the final one will be an empty iterable collection, with the intervening
values the results of successive applications of init
.
Note: Even when applied to a view or a lazy collection it will always force the elements.
- Returns:
an iterator over all the inits of this iterable collection
- Example:
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Tests whether the collection is empty.
Tests whether the collection is empty.
Note: Implementations in subclasses that are not repeatedly traversable must take
care not to consume any elements when isEmpty
is called.
- Returns:
true
if the collection contains no elements,false
otherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Iterator can be used only once
Iterator can be used only once
- Inherited from:
- IterableOnce
- Source:
- IterableOnce.scala
- Returns:
The number of elements in this collection, if it can be cheaply computed, -1 otherwise. Cheaply usually means: Not requiring a collection traversal.
- Inherited from:
- IterableOnce
- Source:
- IterableOnce.scala
Selects the last element.
Selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Returns:
The last element of this iterable collection.
- Throws:
- NoSuchElementException
If the iterable collection is empty.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Optionally selects the last element.
Optionally selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Returns:
the last element of this iterable collection$ if it is nonempty,
None
if it is empty.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Finds the largest element.
Finds the largest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- ord
An ordering to be used for comparing elements.
- Returns:
the largest element of this collection with respect to the ordering
ord
.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the largest value measured by function f.
Finds the first element which yields the largest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- Returns:
the first element of this collection with the largest value measured by function f with respect to the ordering
cmp
.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the largest value measured by function f.
Finds the first element which yields the largest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- Returns:
an option value containing the first element of this collection with the largest value measured by function f with respect to the ordering
cmp
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the largest element.
Finds the largest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- ord
An ordering to be used for comparing elements.
- Returns:
an option value containing the largest element of this collection with respect to the ordering
ord
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the smallest element.
Finds the smallest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- ord
An ordering to be used for comparing elements.
- Returns:
the smallest element of this collection with respect to the ordering
ord
.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the smallest value measured by function f.
Finds the first element which yields the smallest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- Returns:
the first element of this collection with the smallest value measured by function f with respect to the ordering
cmp
.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the smallest value measured by function f.
Finds the first element which yields the smallest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- Returns:
an option value containing the first element of this collection with the smallest value measured by function f with respect to the ordering
cmp
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the smallest element.
Finds the smallest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- ord
An ordering to be used for comparing elements.
- Returns:
an option value containing the smallest element of this collection with respect to the ordering
ord
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Displays all elements of this collection in a string.
Displays all elements of this collection in a string.
Delegates to addString, which can be overridden.
- Returns:
a string representation of this collection. In the resulting string the string representations (w.r.t. the method
toString
) of all elements of this collection follow each other without any separator string.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Displays all elements of this collection in a string using a separator string.
Displays all elements of this collection in a string using a separator string.
Delegates to addString, which can be overridden.
- Value parameters:
- sep
the separator string.
- Returns:
a string representation of this collection. In the resulting string the string representations (w.r.t. the method
toString
) of all elements of this collection are separated by the stringsep
.- Example:
List(1, 2, 3).mkString("|") = "1|2|3"
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Displays all elements of this collection in a string using start, end, and separator strings.
Displays all elements of this collection in a string using start, end, and separator strings.
Delegates to addString, which can be overridden.
- Value parameters:
- end
the ending string.
- sep
the separator string.
- start
the starting string.
- Returns:
a string representation of this collection. The resulting string begins with the string
start
and ends with the stringend
. Inside, the string representations (w.r.t. the methodtoString
) of all elements of this collection are separated by the stringsep
.- Example:
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether the collection is not empty.
Tests whether the collection is not empty.
- Returns:
true
if the collection contains at least one element,false
otherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
A pair of, first, all elements that satisfy predicate p
and, second,
all elements that do not.
A pair of, first, all elements that satisfy predicate p
and, second,
all elements that do not. Interesting because it splits a collection in two.
The default implementation provided here needs to traverse the collection twice.
Strict collections have an overridden version of partition
in StrictOptimizedIterableOps
,
which requires only a single traversal.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Applies a function f
to each element of the iterable collection and returns a pair of iterable collections: the first one
made of those values returned by f
that were wrapped in scala.util.Left, and the second
one made of those wrapped in scala.util.Right.
Applies a function f
to each element of the iterable collection and returns a pair of iterable collections: the first one
made of those values returned by f
that were wrapped in scala.util.Left, and the second
one made of those wrapped in scala.util.Right.
Example:
val xs = Iterable(1, "one", 2, "two", 3, "three") partitionMap {
case i: Int => Left(i)
case s: String => Right(s)
}
// xs == (Iterable(1, 2, 3),
// Iterable(one, two, three))
- Type parameters:
- A1
the element type of the first resulting collection
- A2
the element type of the second resulting collection
- Value parameters:
- f
the 'split function' mapping the elements of this iterable collection to an scala.util.Either
- Returns:
a pair of iterable collections: the first one made of those values returned by
f
that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
the result type of the
*
operator.
- Value parameters:
- num
an implicit parameter defining a set of numeric operations which includes the
*
operator to be used in forming the product.
- Returns:
the product of all elements of this collection with respect to the
*
operator innum
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
The size of this product.
The size of this product.
- Returns:
for a product
A(x1, ..., xk)
, returnsk
- Inherited from:
- Product
- Source:
- Product.scala
The nth element of this product, 0-based.
The nth element of this product, 0-based. In other words, for a
product A(x1, ..., xk)
, returns x(n+1)
where 0 <= n < k
.
- Value parameters:
- n
the index of the element to return
- Returns:
the element
n
elements after the first element- Throws:
- IndexOutOfBoundsException
if the
n
is out of range(n < 0 || n >= productArity).
- Inherited from:
- Product
- Source:
- Product.scala
The name of the nth element of this product, 0-based.
The name of the nth element of this product, 0-based. In the default implementation, an empty string.
- Value parameters:
- n
the index of the element name to return
- Returns:
the name of the specified element
- Throws:
- IndexOutOfBoundsException
if the
n
is out of range(n < 0 || n >= productArity).
- Inherited from:
- Product
- Source:
- Product.scala
An iterator over the names of all the elements of this product.
An iterator over the names of all the elements of this product.
- Inherited from:
- Product
- Source:
- Product.scala
An iterator over all the elements of this product.
An iterator over all the elements of this product.
- Returns:
in the default implementation, an
Iterator[Any]
- Inherited from:
- Product
- Source:
- Product.scala
A string used in the toString
methods of derived classes.
A string used in the toString
methods of derived classes.
Implementations may override this method to prepend a string prefix
to the result of toString
methods.
- Returns:
in the default implementation, the empty string
- Inherited from:
- Product
- Source:
- Product.scala
Reduces the elements of this collection using the specified associative binary operator.
Reduces the elements of this collection using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
- Type parameters:
- B
A type parameter for the binary operator, a supertype of
A
.
- Value parameters:
- op
A binary operator that must be associative.
- Returns:
The result of applying reduce operator
op
between all the elements if the collection is nonempty.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Applies a binary operator to all elements of this collection, going left to right.
Applies a binary operator to all elements of this collection, 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
the result of inserting
op
between consecutive elements of this collection, going left to right:op( op( ... op(x1, x2) ..., xn-1), xn)
wherex1, ..., xn
are the elements of this collection.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Optionally applies a binary operator to all elements of this collection, going left to right.
Optionally applies a binary operator to all elements of this collection, 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
an option value containing the result of
reduceLeft(op)
if this collection is nonempty,None
otherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Reduces the elements of this collection, if any, using the specified associative binary operator.
Reduces the elements of this collection, if any, using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
- Type parameters:
- B
A type parameter for the binary operator, a supertype of
A
.
- Value parameters:
- op
A binary operator that must be associative.
- Returns:
An option value containing result of applying reduce operator
op
between all the elements if the collection is nonempty, andNone
otherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Applies a binary operator to all elements of this collection, going right to left.
Applies a binary operator to all elements of this collection, 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
the result of inserting
op
between consecutive elements of this collection, going right to left:op(x1, op(x2, ..., op(xn-1, xn)...))
wherex1, ..., xn
are the elements of this collection.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Optionally applies a binary operator to all elements of this collection, going right to left.
Optionally applies a binary operator to all elements of this collection, 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
an option value containing the result of
reduceRight(op)
if this collection is nonempty,None
otherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Computes a prefix scan of the elements of the collection.
Computes a prefix scan of the elements of the collection.
Note: The neutral element z
may be applied more than once.
- Type parameters:
- B
element type of the resulting collection
- Value parameters:
- op
the associative operator for the scan
- z
neutral element for the operator
op
- Returns:
a new iterable collection containing the prefix scan of the elements in this iterable collection
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Produces a collection containing cumulative results of applying the operator going right to left.
Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
Note: Even when applied to a view or a lazy collection it will always force the elements.
Example:
List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
- Type parameters:
- B
the type of the elements in the resulting collection
- Value parameters:
- op
the binary operator applied to the intermediate result and the element
- z
the initial value
- Returns:
collection with intermediate results
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
The size of this collection.
The size of this collection.
Note: will not terminate for infinite-sized collections.
- Returns:
the number of elements in this collection.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Compares the size of this iterable collection to the size of another Iterable
.
Compares the size of this iterable collection to the size of another Iterable
.
- Value parameters:
- that
the
Iterable
whose size is compared with this iterable collection's size.
- Returns:
A value
x
wherex < 0 if this.size < that.size x == 0 if this.size == that.size x > 0 if this.size > that.size
The method as implemented here does not call
size
directly; its running time isO(this.size min that.size)
instead ofO(this.size + that.size)
. The method should be overridden if computingsize
is cheap andknownSize
returns-1
.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Compares the size of this iterable collection to a test value.
Compares the size of this iterable collection to a test value.
- Value parameters:
- otherSize
the test value that gets compared with the size.
- Returns:
A value
x
wherex < 0 if this.size < otherSize x == 0 if this.size == otherSize x > 0 if this.size > otherSize
The method as implemented here does not call
size
directly; its running time isO(size min otherSize)
instead ofO(size)
. The method should be overridden if computingsize
is cheap andknownSize
returns-1
.- See also:
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Returns a value class containing operations for comparing the size of this iterable collection to a test value.
Returns a value class containing operations for comparing the size of this iterable collection to a test value.
These operations are implemented in terms of sizeCompare(Int)
, and
allow the following more readable usages:
this.sizeIs < size // this.sizeCompare(size) < 0
this.sizeIs <= size // this.sizeCompare(size) <= 0
this.sizeIs == size // this.sizeCompare(size) == 0
this.sizeIs != size // this.sizeCompare(size) != 0
this.sizeIs >= size // this.sizeCompare(size) >= 0
this.sizeIs > size // this.sizeCompare(size) > 0
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
The returned iterator will be empty when called on an empty collection. The last element the iterator produces may be smaller than the window size when the original collection isn't exhausted by the window before it and its last element isn't skipped by the step before it.
- Value parameters:
- size
the number of elements per group
- step
the distance between the first elements of successive groups
- Returns:
An iterator producing iterable collections of size
size
, except the last element (which may be the only element) will be smaller if there are fewer thansize
elements remaining to be grouped.- See also:
scala.collection.Iterator, method
sliding
- Example:
List(1, 2, 3, 4, 5).sliding(2, 2) = Iterator(List(1, 2), List(3, 4), List(5))
List(1, 2, 3, 4, 5, 6).sliding(2, 3) = Iterator(List(1, 2), List(4, 5))
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Groups elements in fixed size blocks by passing a "sliding window"
over them (as opposed to partitioning them, as is done in grouped
.)
Groups elements in fixed size blocks by passing a "sliding window"
over them (as opposed to partitioning them, as is done in grouped
.)
An empty collection returns an empty iterator, and a non-empty collection containing fewer elements than the window size returns an iterator that will produce the original collection as its only element.
- Value parameters:
- size
the number of elements per group
- Returns:
An iterator producing iterable collections of size
size
, except for a non-empty collection with less thansize
elements, which returns an iterator that produces the source collection itself as its only element.- See also:
scala.collection.Iterator, method
sliding
- Example:
List().sliding(2) = empty iterator
List(1).sliding(2) = Iterator(List(1))
List(1, 2).sliding(2) = Iterator(List(1, 2))
List(1, 2, 3).sliding(2) = Iterator(List(1, 2), List(2, 3))
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Returns a scala.collection.Stepper for the elements of this collection.
Returns a scala.collection.Stepper for the elements of this collection.
The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.
The implicit scala.collection.StepperShape parameter defines the resulting Stepper type according to the element type of this collection.
For collections of
Int
,Short
,Byte
orChar
, an scala.collection.IntStepper is returnedFor collections of
Double
orFloat
, a scala.collection.DoubleStepper is returnedFor collections of
Long
a scala.collection.LongStepper is returnedFor any other element type, an scala.collection.AnyStepper is returned
Note that this method is overridden in subclasses and the return type is refined to
S with EfficientSplit
, for example scala.collection.IndexedSeqOps.stepper. For Steppers marked with
scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters
allow creating parallel streams, whereas bare Steppers can be converted only to sequential
streams.
- Inherited from:
- IterableOnce
- Source:
- IterableOnce.scala
Returns a scala.collection.Stepper for the elements of this collection.
Returns a scala.collection.Stepper for the elements of this collection.
The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.
The implicit scala.collection.StepperShape parameter defines the resulting Stepper type according to the element type of this collection.
For collections of
Int
,Short
,Byte
orChar
, an scala.collection.IntStepper is returnedFor collections of
Double
orFloat
, a scala.collection.DoubleStepper is returnedFor collections of
Long
a scala.collection.LongStepper is returnedFor any other element type, an scala.collection.AnyStepper is returned
Note that this method is overridden in subclasses and the return type is refined to
S with EfficientSplit
, for example scala.collection.IndexedSeqOps.stepper. For Steppers marked with
scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters
allow creating parallel streams, whereas bare Steppers can be converted only to sequential
streams.
- Inherited from:
- IterableOnce
- Source:
- IterableOnce.scala
Sums up the elements of this collection.
Sums up the elements of this collection.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
the result type of the
+
operator.
- Value parameters:
- num
an implicit parameter defining a set of numeric operations which includes the
+
operator to be used in forming the sum.
- Returns:
the sum of all elements of this collection with respect to the
+
operator innum
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
The rest of the collection without its first element.
The rest of the collection without its first element.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Iterates over the tails of this iterable collection.
Iterates over the tails of this iterable collection. The first value will be this
iterable collection and the final one will be an empty iterable collection, with the intervening
values the results of successive applications of tail
.
- Returns:
an iterator over all the tails of this iterable collection
- Example:
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Selects the last n elements.
Selects the last n elements.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Value parameters:
- n
the number of elements to take from this iterable collection.
- Returns:
a iterable collection consisting only of the last
n
elements of this iterable collection, or else the whole iterable collection, if it has less thann
elements. Ifn
is negative, returns an empty iterable collection.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Takes longest prefix of elements that satisfy a predicate.
Takes longest prefix of elements that satisfy a predicate.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Value parameters:
- p
The predicate used to test elements.
- Returns:
the longest prefix of this iterable collection whose elements all satisfy the predicate
p
.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Given a collection factory factory
, convert this collection to the appropriate
representation for the current element type A
.
Given a collection factory factory
, convert this collection to the appropriate
representation for the current element type A
. Example uses:
xs.to(List) xs.to(ArrayBuffer) xs.to(BitSet) // for xs: Iterable[Int]
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Convert collection to array.
Convert collection to array.
Implementation note: DO NOT call Array.from from this method.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Returns:
This collection as a
Seq[A]
. This is equivalent toto(Seq)
but might be faster.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Transposes this iterable collection of iterable collections into a iterable collection of iterable collections.
Transposes this iterable collection of iterable collections into a iterable collection of iterable collections.
The resulting collection's type will be guided by the static type of iterable 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))
Note: Even when applied to a view or a lazy collection it will always force the elements.
- Type parameters:
- B
the type of the elements of each iterable collection.
- Value parameters:
- asIterable
an implicit conversion which asserts that the element type of this iterable collection is an
Iterable
.
- Returns:
a two-dimensional iterable collection of iterable collections which has as nth row the nth column of this iterable collection.
- Throws:
- IllegalArgumentException
if all collections in this iterable collection are not of the same size.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Converts this iterable collection of pairs into two collections of the first and second half of each pair.
Converts this iterable collection of pairs into two collections of the first and second half of each pair.
val xs = Iterable(
(1, "one"),
(2, "two"),
(3, "three")).unzip
// xs == (Iterable(1, 2, 3),
// Iterable(one, two, three))
- Type parameters:
- A1
the type of the first half of the element pairs
- A2
the type of the second half of the element pairs
- Value parameters:
- asPair
an implicit conversion which asserts that the element type of this iterable collection is a pair.
- Returns:
a pair of iterable collections, containing the first, respectively second half of each element pair of this iterable collection.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Converts this iterable collection of triples into three collections of the first, second, and third element of each triple.
Converts this iterable collection of triples into three collections of the first, second, and third element of each triple.
val xs = Iterable(
(1, "one", '1'),
(2, "two", '2'),
(3, "three", '3')).unzip3
// xs == (Iterable(1, 2, 3),
// Iterable(one, two, three),
// Iterable(1, 2, 3))
- Type parameters:
- A1
the type of the first member of the element triples
- A2
the type of the second member of the element triples
- A3
the type of the third member of the element triples
- Value parameters:
- asTriple
an implicit conversion which asserts that the element type of this iterable collection is a triple.
- Returns:
a triple of iterable collections, containing the first, second, respectively third member of each element triple of this iterable collection.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
A view over the elements of this collection.
A view over the elements of this collection.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Creates a non-strict filter of this iterable collection.
Creates a non-strict filter of this iterable 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.
- Value parameters:
- p
the predicate used to test elements.
- Returns:
an object of class
WithFilter
, which supportsmap
,flatMap
,foreach
, andwithFilter
operations. All these operations apply to those elements of this iterable collection which satisfy the predicatep
.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs.
Returns a iterable collection formed from this iterable collection 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.
- Type parameters:
- B
the type of the second half of the returned pairs
- Value parameters:
- that
The iterable providing the second half of each result pair
- Returns:
a new iterable collection containing pairs consisting of corresponding elements of this iterable collection and
that
. The length of the returned collection is the minimum of the lengths of this iterable collection andthat
.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs.
Returns a iterable collection formed from this iterable collection 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.
- Value parameters:
- that
the iterable providing the second half of each result pair
- thatElem
the element to be used to fill up the result if
that
is shorter than this iterable collection.- thisElem
the element to be used to fill up the result if this iterable collection is shorter than
that
.
- Returns:
a new collection of type
That
containing pairs consisting of corresponding elements of this iterable collection andthat
. The length of the returned collection is the maximum of the lengths of this iterable collection andthat
. If this iterable collection is shorter thanthat
,thisElem
values are used to pad the result. Ifthat
is shorter than this iterable collection,thatElem
values are used to pad the result.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Deprecated and Inherited methods
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether this collection is known to have a finite size.
Tests whether this 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.
- Returns:
true
if this collection is known to have finite size,false
otherwise.- See also:
method
knownSize
for a more useful alternative- Deprecated
This method is deprecated in 2.13 because it does not provide any actionable information. As noted above, even the collection library itself does not use it. When there is no guarantee that a collection is finite, it is generally best to attempt a computation anyway and document that it will not terminate for infinite collections rather than backing out because this would prevent performing the computation on collections that are in fact finite even though
hasDefiniteSize
returnsfalse
.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Converts this iterable collection to an unspecified Iterable.
Converts this iterable collection to an unspecified Iterable. Will return the same collection if this instance is already Iterable.
- Returns:
An Iterable containing all elements of this iterable collection.
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
A view over a slice of the elements of this collection.
A view over a slice of the elements of this collection.
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala