Module | Enumerable |
In: |
vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb
vendor/rails/activesupport/lib/active_support/json/encoders/enumerable.rb |
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 vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 79 79: def each_with_object(memo, &block) 80: returning memo do |m| 81: each do |element| 82: block.call(element, m) 83: end 84: end 85: end
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 vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 22 22: def group_by 23: assoc = ActiveSupport::OrderedHash.new 24: 25: each do |element| 26: key = yield(element) 27: 28: if assoc.has_key?(key) 29: assoc[key] << element 30: else 31: assoc[key] = [element] 32: end 33: end 34: 35: assoc 36: 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 ...>, ...}
# File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 94 94: def index_by 95: inject({}) do |accum, elem| 96: accum[yield(elem)] = elem 97: accum 98: end 99: end
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 vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 103 103: def many?(&block) 104: size = block_given? ? select(&block).size : self.size 105: size > 1 106: 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)
# File vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb, line 57 57: def sum(identity = 0, &block) 58: return identity unless size > 0 59: 60: if block_given? 61: map(&block).sum 62: else 63: inject { |sum, element| sum + element } 64: end 65: end