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

Methods

Public Instance methods

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

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"

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 ...>, ...}

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.

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)

[Validate]