Файл: Programming_in_Scala,_2nd_edition.pdf

What it is

What it does

Executes function f for every element of xs.

A collection consisting of the elements of both xs

and ys. ys is a TraversableOnce collection, i.e.,

either a Traversable or an Iterator.

xs.toArray

xs.toList

xs.toIterable

xs.toSeq

xs.toIndexedSeq

xs.toStream

xs.toSet

xs.toMap

Copying:

xs copyToBuffer buf

Copies all elements of the collection to buffer

buf.

xs copyToArray(arr, s, len)

Copies at most len elements of arr, starting at

index s. The last two arguments are optional.

Size info:

xs.isEmpty

Tests whether the collection is empty.

xs.nonEmpty

Tests whether the collection contains elements.

xs.size

The number of elements in the collection.

xs.hasDefiniteSize

True if xs is known to have finite size.

Element retrieval:

xs.head

The first element of the collection (or, some

element, if no order is defined).

xs.headOption

The first element of xs in an option value, or

None if xs is empty.

xs.last

The last element of the collection (or, some

element, if no order is defined).

xs.lastOption

The last element of xs in an option value, or None

if xs is empty.

xs find p

An option containing the first element in xs that

satisfies p, or None if no element qualifies.

Subcollections:

xs.tail

The rest of the collection except xs.head.

xs.init

The rest of the collection except xs.last.

xs slice (from, to)

A collection consisting of elements in some index

range of xs (from from, up to and excluding to).

xs take n

A collection consisting of the first n elements of

xs (or, some arbitrary n elements, if no order is

defined).

xs drop n

The rest of the collection except xs take n.

xs takeWhile p

The longest prefix of elements in the collection

that all satisfy p.

xs dropWhile p

The collection without the longest prefix of

elements that all satisfy p.

Table 24.1 · continued

xs filter p

The collection consisting of those elements of xs

that satisfy the predicate p.

xs withFilter p

A non-strict filter of this collection. All

operations on the resulting filter will only apply

to those elements of xs for which the condition p

is true.

xs filterNot p

The collection consisting of those elements of xs

that do not satisfy the predicate p.

Subdivisions:

xs splitAt n

Splits xs at a position, giving the pair of

collections (xs take n, xs drop n).

xs span p

Splits xs according to a predicate, giving the pair

of collections (xs takeWhile p,

xs.dropWhile p).

xs partition p

Splits xs into a pair of collections; one with

elements that satisfy the predicate p, the other

with elements that do not, giving the pair of

collections (xs filter p, xs.filterNot p).

xs groupBy f

Partitions xs into a map of collections according

to a discriminator function f.

Element conditions:

(z /: xs)(op)

Applies binary operation op between successive

elements of xs, going left to right, starting with z.

(xs :\ z)(op)

Applies binary operation op between successive

elements of xs, going right to left, starting with z.

xs.foldLeft(z)(op)

Same as (z /: xs)(op).

xs.foldRight(z)(op)

Same as (xs :\ z)(op).

Table 24.1 · continued

xs reduceLeft op

Applies binary operation op between successive

elements of non-empty collection xs, going left

to right.

xs reduceRight op

Applies binary operation op between successive

elements of non-empty collection xs, going right

to left.

Specific folds:

xs.sum

The sum of the numeric element values of

collection xs.

xs.product

The product of the numeric element values of

collection xs.

xs.min

The minimum of the ordered element values of

collection xs.

xs.max

The maximum of the ordered element values of

collection xs.

Strings:

xs addString (b, start,

Adds a string to StringBuilder b that shows all

sep, end)

elements of xs between separators sep enclosed

in strings start and end. start, sep, and end

are all optional.

xs mkString (start,

Converts the collection to a string that shows all

sep, end)

elements of xs between separators sep enclosed

in strings start and end. start, sep, and end

are all optional.

xs.stringPrefix

The collection name at the beginning of the string

returned from xs.toString.

Views:

xs.view

Produces a view over xs.

xs view (from, to)

Produces a view that represents the elements in

some index range of xs.