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 def each_with_object(memo) return to_enum :each_with_object, memo unless block_given? each do |element| yield element, memo end memo 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 def exclude?(object) !include?(object) 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 def group_by return to_enum :group_by unless block_given? assoc = ActiveSupport::OrderedHash.new each do |element| key = yield(element) if assoc.has_key?(key) assoc[key] << element else assoc[key] = [element] end end assoc 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 def index_by return to_enum :index_by unless block_given? Hash[map { |elem| [yield(elem), elem] }] 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 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
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 def sum(identity = 0, &block) if block_given? map(&block).sum(identity) else inject(:+) || identity end end