# File activesupport/lib/active_support/core_ext/enumerable.rb, line 60
def exclude?(object)
  !include?(object)
end

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

# File activesupport/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

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 activesupport/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

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 activesupport/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

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)