Module: Enumerable

### Home Classes Methods

### In Files

- lib/active_support/core_ext/enumerable.rb
- lib/active_support/json/encoding.rb

### Methods

- #as_json
- #each_with_object
- #exclude?
- #group_by
- #index_by
- #many?
- #sum

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No matching classes.

# Enumerable

### Public Instance Methods

as_json(options = nil) click to toggle source

    # File lib/active_support/json/encoding.rb, line 202
    def as_json(options = nil) to_a end

each_with_object(memo, &block) click to toggle source

Iterates over a collection, passing the current element and the `memo` to the block. Handy for building up hashes or reducing collections down to one object. Examples:

    %w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase }
    # => {'foo' => 'FOO', 'bar' => 'BAR'}

Note that you can't use immutable objects like numbers, true or false as the memo. You would think the following returns 120, but since the memo is never changed, it does not.

    (1..5).each_with_object(1) { |value, memo| memo *= value } # => 1

    # File lib/active_support/core_ext/enumerable.rb, line 78
    def each_with_object(memo, &block)
      each do |element|
        block.call(element, memo)
      end
      memo
    end

exclude?(object) click to toggle source

The negative of the Enumerable#include?. Returns true if the collection does not include the object.

    # File lib/active_support/core_ext/enumerable.rb, line 107
    def exclude?(object)
      !include?(object)
    end

group_by() click to toggle source

Collect an enumerable into sets, grouped by the result of a block. Useful, for example, for grouping records by date.

Example:

    latest_transcripts.group_by(&:day).each do |day, transcripts|
      p "#{day} -> #{transcripts.map(&:class).join(', ')}"
    end
    "2006-03-01 -> Transcript"
    "2006-02-28 -> Transcript"
    "2006-02-27 -> Transcript, Transcript"
    "2006-02-26 -> Transcript, Transcript"
    "2006-02-25 -> Transcript"
    "2006-02-24 -> Transcript, Transcript"
    "2006-02-23 -> Transcript"

    # File lib/active_support/core_ext/enumerable.rb, line 22
    def group_by
      assoc = ActiveSupport::OrderedHash.new

      each do |element|
        key = yield(element)

        if assoc.has_key?(key)
          assoc[key] << element
        else
          assoc[key] = [element]
        end
      end

      assoc
    end

index_by() click to toggle source

Convert an enumerable to a hash. Examples:

    people.index_by(&:login)
      => { "nextangle" => <Person ...>, "chade-" => <Person ...>, ...}
    people.index_by { |person| "#{person.first_name} #{person.last_name}" }
      => { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}

    # File lib/active_support/core_ext/enumerable.rb, line 92
    def index_by
      inject({}) do |accum, elem|
        accum[yield(elem)] = elem
        accum
      end
    end

many?(&block) click to toggle source

Returns true if the collection has more than 1 element. Functionally equivalent to collection.size > 1. Works with a block too ala any?, so people.many? { |p| p.age > 26 } # => returns true if more than 1 person is over 26.

    # File lib/active_support/core_ext/enumerable.rb, line 101
    def many?(&block)
      size = block_given? ? select(&block).size : self.size
      size > 1
    end

sum(identity = 0, &block) click to toggle source

Calculates a sum from the elements. Examples:

    payments.sum { |p| p.price * p.tax_rate }
    payments.sum(&:price)

The latter is a shortcut for:

    payments.inject(0) { |sum, p| sum + p.price }

It can also calculate the sum without the use of a block.

    [5, 15, 10].sum # => 30
    ["foo", "bar"].sum # => "foobar"
    [[1, 2], [3, 1, 5]].sum => [1, 2, 3, 1, 5]

The default sum of an empty list is zero. You can override this default:

    [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)

    # File lib/active_support/core_ext/enumerable.rb, line 57
    def sum(identity = 0, &block)
      if block_given?
        map(&block).sum(identity)
      else
        inject { |sum, element| sum + element } || identity
      end
    end

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