module Enumerable(T)

Overview

The Enumerable mixin provides collection classes with several traversal, searching, filtering and querying methods.

Including types must provide an each method, which yields successive members of the collection.

For example:

class Three
  include Enumerable(Int32)

  def each(&)
    yield 1
    yield 2
    yield 3
  end
end

three = Three.new
three.to_a                # => [1, 2, 3]
three.select &.odd?       # => [1, 3]
three.all? { |x| x < 10 } # => true

Note that most search and filter methods traverse an Enumerable eagerly, producing an Array as the result. For a lazy alternative refer to the Iterator and Iterable modules.

Direct including types

• Hash(K, V)
• Range(B, E)

Defined in:

Instance Method Summary

• #avg

  Returns the average of a collection of numbers.

• #blank?

  An enumerable is blank if it's empty.

• #exactly?(count : Int32, &)

  Checks if exactly n elements meet a certain predicate with a block.

• #excludes?(obj)

  Returns true if the collection does not contains obj, false otherwise.

• #frequencies

  Counts the number of occurrence of items in the enumerable.

• #many?(&)

  Returns true if many elements fulfilled the block condition, much like any?, so people.many? { |p| p.age > 26 } returns true if more than one person is over 26.

• #many?

  Returns true if the enumerable has more than 1 element.

• #pluck(*keys)

  Convert an enumerable to an array based on the given key, throws an error if any key does not exists.

• #pluck?(*keys)

  Convert an enumerable to an array based on the given key, returns nil if any key does not exists.

• #without(*items)

  Returns a copy of the enumerable without the specified items.

Instance Method Detail

[1, 2, 3, 4, 5].avg
=> 3

[1,2,3].blank?
=> false
[].blank?
=> true

  [1, 2, 3, 4].exactly?(1) { |n| n > 3 } #=> true
  [1, 2, 3, 4].exactly?(2, &.even?) #=> true
  [1, 1, 3, 3].exactly?(2, &.even?) #=> false

[1, 2, 3].excludes?(4) # => true
[1, 2, 3].excludes?(3) # => false

  [].frequencies # => {}
  [1, :symbol, 'string', 3, :symbol, 1].frequencies
    #=> { 1 => 2, :symbol => 2, 'string' => 1, 3 => 1 }

[{ name: "David" }, { name: "Rafael" }, { name: "Aaron" }].pluck(:name)
=> ["David", "Rafael", "Aaron"]

[{ id: 1, name: "David" }, { id: 2, name: "Rafael" }].pluck(:id, :name)
=> [{1, "David"}, {2, "Rafael"}]

[{ name: "David" }, { name: "Rafael" }, { name: "Aaron" }].pluck(:name)
=> ["David", "Rafael", "Aaron"]

[{ id: 1, name: "David" }, { id: 2, name: "Rafael" }].pluck(:id, :name)
=> [{1, "David"}, {2, "Rafael"}]

[{ id: 1, name: "David" }, { id: 2, name: "Rafael" }].pluck(:color)
=> []

[{ id: 1, name: "David" }, { id: 2, name: "Rafael" }].pluck(:id, :color)
=> [{1, nil}, {2, nil}]

[1, 2, 3, 4, 5].without 3, 5
=> [1, 2, 4]