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 lib/active_support/core_ext/enumerable.rb, line 79 79: def each_with_object(memo) 80: return to_enum :each_with_object, memo unless block_given? 81: each do |element| 82: yield element, memo 83: end 84: memo 85: end
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 114 114: def exclude?(object) 115: !include?(object) 116: 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 lib/active_support/core_ext/enumerable.rb, line 22 22: def group_by 23: return to_enum :group_by unless block_given? 24: assoc = ActiveSupport::OrderedHash.new 25: 26: each do |element| 27: key = yield(element) 28: 29: if assoc.has_key?(key) 30: assoc[key] << element 31: else 32: assoc[key] = [element] 33: end 34: end 35: 36: assoc 37: 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 lib/active_support/core_ext/enumerable.rb, line 94 94: def index_by 95: return to_enum :index_by unless block_given? 96: Hash[map { |elem| [yield(elem), elem] }] 97: 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 lib/active_support/core_ext/enumerable.rb, line 101 101: def many? 102: cnt = 0 103: if block_given? 104: any? do |element| 105: cnt += 1 if yield element 106: cnt > 1 107: end 108: else 109: any?{ (cnt += 1) > 1 } 110: end 111: 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(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 58 58: def sum(identity = 0, &block) 59: if block_given? 60: map(&block).sum(identity) 61: else 62: inject(:+) || identity 63: end 64: end
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