Module Enumerable
In: vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb
vendor/rails/activesupport/lib/active_support/json/encoders/enumerable.rb

Methods

group_by   index_by   sum  

Public Instance methods

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"

[Source]

    # File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 20
20:   def group_by
21:     inject ActiveSupport::OrderedHash.new do |grouped, element|
22:       (grouped[yield(element)] ||= []) << element
23:       grouped
24:     end
25:   end

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 ...>, ...}

[Source]

    # File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 63
63:   def index_by
64:     inject({}) do |accum, elem|
65:       accum[yield(elem)] = elem
66:       accum
67:     end
68:   end

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 { |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)

[Source]

    # File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 46
46:   def sum(identity = 0, &block)
47:     return identity unless size > 0
48: 
49:     if block_given?
50:       map(&block).sum
51:     else
52:       inject { |sum, element| sum + element }
53:     end
54:   end

[Validate]