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 77 def each_with_object(memo, &block) memo.tap do |m| each do |element| block.call(element, m) end end 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 117 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 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 92 def index_by inject({}) do |accum, elem| accum[yield(elem)] = elem accum end 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 lib/active_support/core_ext/enumerable.rb, line 101 def many?(&block) size = block_given? ? select(&block).size : self.size size > 1 end
Returns true if none of the elements match the given block.
success = responses.none? {|r| r.status / 100 == 5 }
This is a builtin method in Ruby 1.8.7 and later.
# File lib/active_support/core_ext/enumerable.rb, line 111 def none?(&block) !any?(&block) 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 lib/active_support/core_ext/enumerable.rb, line 57 def sum(identity = 0, &block) if block_given? map(&block).sum(identity) else inject { |sum, element| sum + element } || identity end end
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