The sequence traits Seq, IndexedSeq, and LinearSeq Contents

The sequence traits `Seq`, `IndexedSeq`, and `LinearSeq`

The Seq trait represents sequences. A sequence is a kind of iterable that has a length and whose elements have fixed index positions, starting from 0.

The operations on sequences, summarized in the following figure, fall into the following categories:

Indexing and length operations apply, isDefinedAt, length, indices, and lengthCompare. For a Seq, the apply operation means indexing; hence a sequence of type Seq[T] is a partial function that takes an Int argument (an index) and which yields a sequence element of type T. In other words Seq[T] extends PartialFunction[Int, T]. The elements of a sequence are indexed from zero up to the length of the sequence minus one. The length method on sequences is an alias of the size method of general collections. The lengthCompare method allows you to compare the lengths of two sequences even if one of the sequences has infinite length.
Index search operations indexOf, lastIndexOf, indexofSlice, lastIndexOfSlice, indexWhere, lastIndexWhere, segmentLength, prefixLength, which return the index of an element equal to a given value or matching some predicate.
Addition operations +:, :+, padTo, which return new sequences obtained by adding elements at the front or the end of a sequence.
Update operations updated, patch, which return a new sequence obtained by replacing some elements of the original sequence.
Sorting operations sorted, sortWith, sortBy, which sort sequence elements according to various criteria.
Reversal operations reverse, reverseIterator, reverseMap, which yield or process sequence elements in reverse order.
Comparisons startsWith, endsWith, contains, containsSlice, corresponds, which relate two sequences or search an element in a sequence.
Multiset operations intersect, diff, union, distinct, which perform set-like operations on the elements of two sequences or remove duplicates.

If a sequence is mutable, it offers in addition a side-effecting update method, which lets sequence elements be updated. As always in Scala, syntax like seq(idx) = elem is just a shorthand for seq.update(idx, elem), so update gives convenient assignment syntax for free. Note the difference between update and updated. update changes a sequence element in place, and is only available for mutable sequences. updated is available for all sequences and always returns a new sequence instead of modifying the original.

Operations in class Seq
What it is	What it does
Indexing and Length:
`xs(i)`	(or, written out, `xs` `apply` `i`). The element of `xs` at index `i`.
`xs` `isDefinedAt` `i`	Tests whether `i` is contained in `xs.indices`.
`xs.length`	The length of the sequence (same as `size`).
`xs.lengthCompare` `ys`	Returns `-1` if `xs` is shorter than `ys`, `+1` if it is longer, and `0` is they have the same length. Works even if one if the sequences is infinite.
`xs.indices`	The index range of `xs`, extending from 0 to `xs.length` `-` `1`.
Index Search:
`xs` `indexOf` `x`	The index of the first element in `xs` equal to `x` (several variants exist).
`xs` `lastIndexOf` `x`	The index of the last element in `xs` equal to `x` (several variants exist).
`xs` `indexOfSlice` `ys`	The first index of `xs` such that successive elements starting from that index form the sequence `ys`.
`xs` `lastIndexOfSlice` `ys`	The last index of `xs` such that successive elements starting from that index form the sequence `ys`.
`xs` `indexWhere` `p`	The index of the first element in `xs` that satisfies `p` (several variants exist).
`xs` `segmentLength` `(p,` `i)`	The length of the longest uninterrupted segment of elements in `xs`, starting with `xs(i)`, that all satisfy the predicate `p`.
`xs` `prefixLength` `p`	The length of the longest prefix of elements in `xs` that all satisfy the predicate `p`.
Additions:
`x` `+:` `xs`	A new sequence that consists of `x` prepended to `xs`.
`xs` `:+` `x`	A new sequence that consists of `x` append to `xs`.
`xs` `padTo` `(len,` `x)`	The sequence resulting from appending the value `x` to `xs` until length `len` is reached.
Updates:
`xs` `patch` `(i,` `ys,` `r)`	The sequence resulting from replacing `r` elements of `xs` starting with `i` by the patch `ys`.
`xs` `updated` `(i,` `x)`	A copy of `xs` with the element at index `i` replaced by `x`.
`xs(i)` `=` `x`	(or, written out, `xs.update(i,` `x)`, only available for `mutable.Seq`s). Changes the element of `xs` at index `i` to `y`.
Sorting:
`xs.sorted`	A new sequence obtained by sorting the elements of `xs` using the standard ordering of the element type of `xs`.
`xs` `sortWith` `lt`	A new sequence obtained by sorting the elements of `xs` using `lt` as comparison operation.
`xs` `sortBy` `f`	A new sequence obtained by sorting the elements of `xs`. Comparison between two elements proceeds by mapping the function `f` over both and comparing the results.
Reversals:
`xs.reverse`	A sequence with the elements of `xs` in reverse order.
`xs.reverseIterator`	An iterator yielding all the elements of `xs` in reverse order.
`xs` `reverseMap` `f`	A sequence obtained by mapping `f` over the elements of `xs` in reverse order.
Comparisons:
`xs` `startsWith` `ys`	Tests whether `xs` starts with sequence `ys` (several variants exist).
`xs` `endsWith` `ys`	Tests whether `xs` ends with sequence `ys` (several variants exist).
`xs` `contains` `x`	Tests whether `xs` has an element equal to `x`.
`xs` `containsSlice` `ys`	Tests whether `xs` has a contiguous subsequence equal to `ys`.
`(xs` `corresponds` `ys)(p)`	Tests whether corresponding elements of `xs` and `ys` satisfy the binary predicate `p`.
Multiset Operations:
`xs` `intersect` `ys`	The multi-set intersection of sequences `xs` and `ys` that preserves the order of elements in `xs`.
`xs` `diff` `ys`	The multi-set difference of sequences `xs` and `ys` that preserves the order of elements in `xs`.
`xs` `union` `ys`	Multiset union; same as `xs` `++` `ys`.
`xs.distinct`	A subsequence of `xs` that contains no duplicated element.

Trait Seq has two subtraits LinearSeq, and IndexedSeq. These do not add any new operations, but each offers different performance characteristics: A linear sequence has efficient head and tail operations, whereas an indexed sequence has efficient apply, length, and (if mutable) update operations. Frequently used linear sequences are scala.collection.immutable.List and scala.collection.immutable.Stream. Frequently used indexed sequences are scala.Array and scala.collection.mutable.ArrayBuffer. The Vector class provides an interesting compromise between indexed and linear access. It has both effectively constant time indexing overhead and constant time linear access overhead. Because if this, vectors are a good foundation for mixed access patterns where both indexed and linear accesses are used. You'll learn more on vectors elsewhere

Buffers

The sequence traits Seq, IndexedSeq, and LinearSeq Contents

The sequence traits Seq, IndexedSeq, and LinearSeq

The sequence traits `Seq`, `IndexedSeq`, and `LinearSeq`