module Enumerable - activesupport-4.2.3 Documentation

# module Enumerable

### Public Instance Methods

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 60
    def exclude?(object)
      !include?(object)
    end

index_by() { |elem| ... } click to toggle source

Convert an enumerable to a hash.

    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 34
    def index_by
      if block_given?
        Hash[map { |elem| [yield(elem), elem] }]
      else
        to_enum(:index_by) { size if respond_to?(:size) }
      end
    end

many?() { |element| ... } click to toggle source

Returns `true` if the enumerable has more than 1 element. Functionally equivalent to `enum.to_a.size > 1`. Can be called with a block too, much like any?, so `people.many? { |p| p.age > 26 }` returns `true` if more than one person is over 26.

    # File lib/active_support/core_ext/enumerable.rb, line 46
    def many?
      cnt = 0
      if block_given?
        any? do |element|
          cnt += 1 if yield element
          cnt > 1
        end
      else
        any? { (cnt += 1) > 1 }
      end
    end

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

Calculates a sum from the elements.

    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 20
    def sum(identity = 0, &block)
      if block_given?
        map(&block).sum(identity)
      else
        inject { |sum, element| sum + element } || identity
      end
    end