Get the element at the specified index. This operation is provided for convenience in Seq. It should not be assumed to be efficient unless you have an IndexedSeq.

Defines how to turn a given Iterable[A] into a collection of type C.

This process can be done in a strict way or a non-strict way (ie. without evaluating the elements of the resulting collections). In other words, this methods defines the evaluation model of the collection.

Returns the runtime class representation of the object.

The companion object of this sequence, providing various factory methods.

Iterator can be used only once

The length (number of elements) of the sequence. size is an alias for length in Seq collections.

Test two objects for inequality.

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.

Alias for concat

Alias for prependedAll

Alias for prepended.

Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.

Alias for appended

Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.

Alias for appendedAll

Test two objects for equality. The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

Appends all elements of this sequence to a string builder. The written text consists of the string representations (w.r.t. the method toString) of all elements of this sequence 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

Appends all elements of this sequence 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 sequence, 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

Appends all elements of this sequence 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 sequence 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)

A copy of this sequence with an element appended.

Note: will not terminate for infinite-sized collections.

Example:

scala> val a = List(1)
a: List[Int] = List(1)

scala> val b = a :+ 2
b: List[Int] = List(1, 2)

scala> println(a)
List(1)

Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the sequence is the most specific superclass encompassing the element types of the two operands.

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.

Builds a new sequence by applying a partial function to all elements of this sequence on which the function is defined.

Finds the first element of the sequence for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

Iterates over combinations of elements.

A combination of length n is a sequence of n elements selected in order of their first index in this sequence.

For example, "xyx" has two combinations of length 2. The x is selected first: "xx", "xy". The sequence "yx" is not returned as a combination because it is subsumed by "xy".

If there is more than one way to generate the same combination, only one will be returned.

For example, the result "xy" arbitrarily selected one of the x elements.

As a further illustration, "xyxx" has three different ways to generate "xy" because there are three elements x to choose from. Moreover, there are three unordered pairs "xx" but only one is returned.

It is not specified which of these equal combinations is returned. It is an implementation detail that should not be relied on. For example, the combination "xx" does not necessarily contain the first x in this sequence. This behavior is observable if the elements compare equal but are not identical.

As a consequence, "xyx".combinations(3).next() is "xxy": the combination does not reflect the order of the original sequence, but the order in which elements were selected, by "first index"; the order of each x element is also arbitrary.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the sequence is the most specific superclass encompassing the element types of the two operands.

Tests whether this sequence contains a given value as an element.

Note: may not terminate for infinite-sized collections.

Tests whether this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

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 sequence.

Copying will stop once either all the elements of this sequence have been copied, or the end of the array is reached, or len elements have been copied.

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this sequence.

Copying will stop once either all the elements of this sequence have been copied, or the end of the array is reached.

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this sequence.

Copying will stop once either all the elements of this sequence have been copied, or the end of the array is reached.

Tests whether every element of this sequence relates to the corresponding element of another sequence 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.

Counts the number of elements in the sequence which satisfy a predicate.

Note: will not terminate for infinite-sized collections.

Computes the multiset difference between this sequence and another sequence.

Selects all the elements of this sequence ignoring the duplicates.

Selects all the elements of this sequence ignoring the duplicates as determined by == after applying the transforming function f.

Selects all elements except first n ones.

The rest of the collection without its n last elements. For linear, immutable collections this should avoid making a copy.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Drops longest prefix of elements that satisfy a predicate.

The empty iterable of the same type as this iterable

Tests whether this sequence ends with the given sequence.

Note: will not terminate for infinite-sized collections.

Compares the receiver object (this) with the argument object (that) for equivalence.

Any implementation of this method should be an equivalence relation:

• It is reflexive: for any instance 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)).

Tests whether a predicate holds for at least one element of this sequence.

Note: may not terminate for infinite-sized collections.

Selects all elements of this sequence which satisfy a predicate.

Selects all elements of this sequence which do not satisfy a predicate.

Finds the first element of the sequence satisfying a predicate, if any.

Note: may not terminate for infinite-sized collections.

Finds the last element of the sequence satisfying a predicate, if any.

Note: will not terminate for infinite-sized collections.

Builds a new sequence by applying a function to all elements of this sequence and using the elements of the resulting collections.

For example:

def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")

The type of the resulting collection is guided by the static type of sequence. This might cause unexpected results sometimes. For example:

// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)

// lettersOf will return a Set[Char], not a Seq
def lettersOf(words: Seq[String]) = words.toSet flatMap ((word: String) => word.toSeq)

// xs will be an Iterable[Int]
val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)

// ys will be a Map[Int, Int]
val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)

Converts this sequence of iterable collections into a sequence formed by the elements of these iterable collections.

The resulting collection's type will be guided by the type of sequence. For example:

val xs = List(
           Set(1, 2, 3),
           Set(1, 2, 3)
         ).flatten
// xs == List(1, 2, 3, 1, 2, 3)

val ys = Set(
           List(1, 2, 3),
           List(3, 2, 1)
         ).flatten
// ys == Set(1, 2, 3)

Folds the elements of this sequence 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.

Applies a binary operator to a start value and all elements of this sequence, going left to right.

Note: will not terminate for infinite-sized collections.

Applies a binary operator to all elements of this sequence and a start value, going right to left.

Note: will not terminate for infinite-sized collections.

Tests whether a predicate holds for all elements of this sequence.

Note: may not terminate for infinite-sized collections.

Apply f to each element for its side effects Note: [U] parameter needed to help scalac's type inference.

Partitions this sequence into a map of sequences according to some discriminator function.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Partitions this sequence into a map of sequences 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.

Partitions this sequence 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.

Partitions elements in fixed size sequences.

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.

Selects the first element of this sequence.

Optionally selects the first element.

Finds index of first occurrence of some value in this sequence.

Finds index of first occurrence of some value in this sequence after or at some start index.

Finds first index where this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

Finds first index after or at a start index where this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

Finds index of the first element satisfying some predicate.

Note: may not terminate for infinite-sized collections.

Finds index of the first element satisfying some predicate after or at some start index.

Note: may not terminate for infinite-sized collections.

Produces the range of all indices of this sequence.

Note: Even when applied to a view or a lazy collection it will always force the elements.

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.

Iterates over the inits of this sequence. The first value will be this sequence and the final one will be an empty sequence, with the intervening values the results of successive applications of init.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Computes the multiset intersection between this sequence and another sequence.

Tests whether this sequence contains given index.

The implementations of methods apply and isDefinedAt turn a Seq[A] into a PartialFunction[Int, A].

Tests whether the sequence is empty.

Note: Implementations in subclasses that are not repeatedly iterable must take care not to consume any elements when isEmpty is called.

Test whether the dynamic type of the receiver object has the same erasure as T0.

Depending on what T0 is, the test is done in one of the below ways:

• T0 is a non-parameterized class type, e.g. BigDecimal: this method returns true if the value of the receiver object is a BigDecimal or a subtype of BigDecimal.
• T0 is a parameterized class type, e.g. List[Int]: this method returns true if the value of the receiver object is some List[X] for any X. For example, List(1, 2, 3).isInstanceOf[List[String]] will return true.
• T0 is some singleton type x.type or literal x: this method returns this.eq(x). For example, x.isInstanceOf[1] is equivalent to x.eq(1)
• T0 is an intersection X with Y or X & Y: this method is equivalent to x.isInstanceOf[X] && x.isInstanceOf[Y]
• T0 is a union X | Y: this method is equivalent to x.isInstanceOf[X] || x.isInstanceOf[Y]
• T0 is a type parameter or an abstract type member: this method is equivalent to isInstanceOf[U] where U is T0's upper bound, Any if T0 is unbounded. For example, x.isInstanceOf[A] where A is an unbounded type parameter will return true for any value of x.

This is exactly equivalent to the type pattern _: T0

Tests whether this sequence can be repeatedly traversed. Always true for Iterables and false for Iterators unless overridden.

Selects the last element.

Finds index of last occurrence of some value in this sequence before or at a given end index.

Note: will not terminate for infinite-sized collections.

Finds last index where this sequence contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

Finds last index before or at a given end index where this sequence contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

Finds index of last element satisfying some predicate.

Note: will not terminate for infinite-sized collections.

Finds index of last element satisfying some predicate before or at given end index.

Note: will not terminate for infinite-sized collections.

Optionally selects the last element.

Compares the length of this sequence to the size of another Iterable.

Compares the length of this sequence to a test value.

Returns a value class containing operations for comparing the length of this sequence to a test value.

These operations are implemented in terms of lengthCompare(Int), and allow the following more readable usages:

this.lengthIs < len     // this.lengthCompare(len) < 0
this.lengthIs <= len    // this.lengthCompare(len) <= 0
this.lengthIs == len    // this.lengthCompare(len) == 0
this.lengthIs != len    // this.lengthCompare(len) != 0
this.lengthIs >= len    // this.lengthCompare(len) >= 0
this.lengthIs > len     // this.lengthCompare(len) > 0

Builds a new sequence by applying a function to all elements of this sequence.

Finds the largest element.

Note: will not terminate for infinite-sized collections.

Finds the first element which yields the largest value measured by function f.

Note: will not terminate for infinite-sized collections.

Finds the first element which yields the largest value measured by function f.

Note: will not terminate for infinite-sized collections.

Finds the largest element.

Note: will not terminate for infinite-sized collections.

Finds the smallest element.

Note: will not terminate for infinite-sized collections.

Finds the first element which yields the smallest value measured by function f.

Note: will not terminate for infinite-sized collections.

Finds the first element which yields the smallest value measured by function f.

Note: will not terminate for infinite-sized collections.

Finds the smallest element.

Note: will not terminate for infinite-sized collections.

Displays all elements of this sequence in a string.

Delegates to addString, which can be overridden.

Displays all elements of this sequence in a string using a separator string.

Delegates to addString, which can be overridden.

Displays all elements of this sequence in a string using start, end, and separator strings.

Delegates to addString, which can be overridden.

Tests whether the sequence is not empty.

A copy of this sequence with an element value appended until a given target length is reached.

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.

Applies a function f to each element of the sequence and returns a pair of sequences: 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 = `Seq`(1, "one", 2, "two", 3, "three") partitionMap {
 case i: Int => Left(i)
 case s: String => Right(s)
}
// xs == (`Seq`(1, 2, 3),
//        `Seq`(one, two, three))

Produces a new sequence where a slice of elements in this sequence is replaced by another sequence.

Patching at negative indices is the same as patching starting at 0. Patching at indices at or larger than the length of the original sequence appends the patch to the end. If more values are replaced than actually exist, the excess is ignored.

Iterates over distinct permutations of elements.

Note: Even when applied to a view or a lazy collection it will always force the elements.

A copy of the sequence with an element prepended.

Also, the original sequence is not modified, so you will want to capture the result.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = 2 +: x
y: List[Int] = List(2, 1)

scala> println(x)
List(1)

As with :++, returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from :++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

Multiplies up the elements of this collection.

Note: will not terminate for infinite-sized collections.

Reduces the elements of this sequence using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

Applies a binary operator to all elements of this sequence, going left to right.

Note: will not terminate for infinite-sized collections.

Optionally applies a binary operator to all elements of this sequence, going left to right.

Note: will not terminate for infinite-sized collections.

Reduces the elements of this sequence, if any, using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

Applies a binary operator to all elements of this sequence, going right to left.

Note: will not terminate for infinite-sized collections.

Optionally applies a binary operator to all elements of this sequence, going right to left.

Note: will not terminate for infinite-sized collections.

Returns new sequence with elements in reversed order.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

An iterator yielding elements in reversed order.

Note: will not terminate for infinite-sized collections.

Note: xs.reverseIterator is the same as xs.reverse.iterator but might be more efficient.

Are the elements of this collection the same (and in the same order) as those of that?

Computes a prefix scan of the elements of the collection.

Note: The neutral element z may be applied more than once.

Produces a sequence containing cumulative results of applying the operator going left to right, including the initial value.

Note: will not terminate for infinite-sized collections.

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: 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)

Search within an interval in this sorted sequence for a specific element. If this sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.

The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.

Search this sorted sequence for a specific element. If the sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.

The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.

Computes the length of the longest segment that starts from some index and whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

Computes the length of the longest segment that starts from the first element and whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

The size of this sequence.

Note: will not terminate for infinite-sized collections.

Compares the size of this sequence to the size of another Iterable.

Compares the size of this sequence to a test value.

Returns a value class containing operations for comparing the size of this sequence 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

Selects an interval of elements. The returned sequence is made up of all elements x which satisfy the invariant:

from <= indexOf(x) < until

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.

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.

Sorts this sequence according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.

Sorts this sequence according to a comparison function.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

The sort is stable. That is, elements that are equal (as determined by lt) appear in the same order in the sorted sequence as in the original.

Sorts this sequence according to an Ordering.

The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.

Splits this sequence into a prefix/suffix pair according to a predicate.

Note: c span p is equivalent to (but possibly more efficient than) (c takeWhile p, c dropWhile p), provided the evaluation of the predicate p does not cause any side-effects.

Splits this sequence into a prefix/suffix pair at a given position.

Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n).

Tests whether this sequence contains the given sequence at a given index.

Note: If the both the receiver object this and the argument that are infinite sequences this method may not terminate.

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 or Char, an scala.collection.IntStepper is returned
• For collections of Double or Float, a scala.collection.DoubleStepper is returned
• For collections of Long a scala.collection.LongStepper is returned
• For 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.

Sums up the elements of this collection.

Note: will not terminate for infinite-sized collections.

The rest of the collection without its first element.

Iterates over the tails of this sequence. The first value will be this sequence and the final one will be an empty sequence, with the intervening values the results of successive applications of tail.

Selects the first n elements.

A collection containing the last n elements of this collection.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Takes longest prefix of elements that satisfy a predicate.

Applies a side-effecting function to each element in this collection. Strict collections will apply f to their elements immediately, while lazy collections like Views and LazyLists will only apply f on each element if and when that element is evaluated, and each time that element is evaluated.

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]

Convert collection to array.

Implementation note: DO NOT call Array.from from this method.