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
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# File activesupport/lib/active_support/core_ext/enumerable.rb, line 77 77: def each_with_object(memo, &block) 78: returning memo do |m| 79: each do |element| 80: block.call(element, m) 81: end 82: end 83: end
The negative of the Enumerable#include?. Returns true if the collection does not include the object.
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# File activesupport/lib/active_support/core_ext/enumerable.rb, line 117 117: def exclude?(object) 118: !include?(object) 119: 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"
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# File 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 ...>, ...}
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# File activesupport/lib/active_support/core_ext/enumerable.rb, line 92 92: def index_by 93: inject({}) do |accum, elem| 94: accum[yield(elem)] = elem 95: accum 96: end 97: 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.
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# File activesupport/lib/active_support/core_ext/enumerable.rb, line 101 101: def many?(&block) 102: size = block_given? ? select(&block).size : self.size 103: size > 1 104: 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.
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# File activesupport/lib/active_support/core_ext/enumerable.rb, line 111 111: def none?(&block) 112: !any?(&block) 113: 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)
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# File activesupport/lib/active_support/core_ext/enumerable.rb, line 57 57: def sum(identity = 0, &block) 58: if block_given? 59: map(&block).sum(identity) 60: else 61: inject { |sum, element| sum + element } || identity 62: end 63: end