vendor/rails/activesupport/lib/active_support/core_ext/enumerable.rb

   1 require 'active_support/ordered_hash'
   2
   3 module Enumerable
   4   # Ruby 1.8.7 introduces group_by, but the result isn't ordered. Override it.
   5   remove_method(:group_by) if [].respond_to?(:group_by) && RUBY_VERSION < '1.9'
   6
   7   # Collect an enumerable into sets, grouped by the result of a block. Useful,
   8   # for example, for grouping records by date.
   9   #
  10   # Example:
  11   #
  12   #   latest_transcripts.group_by(&:day).each do |day, transcripts|
  13   #     p "#{day} -> #{transcripts.map(&:class).join(', ')}"
  14   #   end
  15   #   "2006-03-01 -> Transcript"
  16   #   "2006-02-28 -> Transcript"
  17   #   "2006-02-27 -> Transcript, Transcript"
  18   #   "2006-02-26 -> Transcript, Transcript"
  19   #   "2006-02-25 -> Transcript"
  20   #   "2006-02-24 -> Transcript, Transcript"
  21   #   "2006-02-23 -> Transcript"
  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 unless [].respond_to?(:group_by)
  37
  38   # Calculates a sum from the elements. Examples:
  39   #
  40   #  payments.sum { |p| p.price * p.tax_rate }
  41   #  payments.sum(&:price)
  42   #
  43   # The latter is a shortcut for:
  44   #
  45   #  payments.inject { |sum, p| sum + p.price }
  46   #
  47   # It can also calculate the sum without the use of a block.
  48   #
  49   #  [5, 15, 10].sum # => 30
  50   #  ["foo", "bar"].sum # => "foobar"
  51   #  [[1, 2], [3, 1, 5]].sum => [1, 2, 3, 1, 5]
  52   #
  53   # The default sum of an empty list is zero. You can override this default:
  54   #
  55   #  [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
  56   #
  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
  66
  67   # Iterates over a collection, passing the current element *and* the
  68   # +memo+ to the block. Handy for building up hashes or
  69   # reducing collections down to one object. Examples:
  70   #
  71   #   %w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase } #=> {'foo' => 'FOO', 'bar' => 'BAR'}
  72   #
  73   # *Note* that you can't use immutable objects like numbers, true or false as
  74   # the memo. You would think the following returns 120, but since the memo is
  75   # never changed, it does not.
  76   #
  77   #   (1..5).each_with_object(1) { |value, memo| memo *= value } # => 1
  78   #
  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 unless [].respond_to?(:each_with_object)
  86
  87   # Convert an enumerable to a hash. Examples:
  88   #
  89   #   people.index_by(&:login)
  90   #     => { "nextangle" => <Person ...>, "chade-" => <Person ...>, ...}
  91   #   people.index_by { |person| "#{person.first_name} #{person.last_name}" }
  92   #     => { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}
  93   #
  94   def index_by
  95     inject({}) do |accum, elem|
  96       accum[yield(elem)] = elem
  97       accum
  98     end
  99   end
 100
 101   # Returns true if the collection has more than 1 element. Functionally equivalent to collection.size > 1.
 102   # Works with a block too ala any?, so people.many? { |p| p.age > 26 } # => returns true if more than 1 person is over 26.
 103   def many?(&block)
 104     size = block_given? ? select(&block).size : self.size
 105     size > 1
 106   end
 107 end