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      if block_given?
  59        map(&block).sum(identity)
  60      else
  61        inject { |sum, element| sum + element } || identity
  62      end
  63    end
  64 
  65    # Iterates over a collection, passing the current element *and* the
  66    # +memo+ to the block. Handy for building up hashes or
  67    # reducing collections down to one object. Examples:
  68    #
  69    #   %w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase } #=> {'foo' => 'FOO', 'bar' => 'BAR'}
  70    #
  71    # *Note* that you can't use immutable objects like numbers, true or false as
  72    # the memo. You would think the following returns 120, but since the memo is
  73    # never changed, it does not.
  74    #
  75    #   (1..5).each_with_object(1) { |value, memo| memo *= value } # => 1
  76    #
  77    def each_with_object(memo, &block)
  78      memo.tap do |m|
  79        each do |element|
  80          block.call(element, m)
  81        end
  82      end
  83    end unless [].respond_to?(:each_with_object)
  84 
  85    # Convert an enumerable to a hash. Examples:
  86    #
  87    #   people.index_by(&:login)
  88    #     => { "nextangle" => <Person ...>, "chade-" => <Person ...>, ...}
  89    #   people.index_by { |person| "#{person.first_name} #{person.last_name}" }
  90    #     => { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}
  91    # 
  92    def index_by
  93      inject({}) do |accum, elem|
  94        accum[yield(elem)] = elem
  95        accum
  96      end
  97    end
  98    
  99    # Returns true if the collection has more than 1 element. Functionally equivalent to collection.size > 1.
 100    # Works with a block too ala any?, so people.many? { |p| p.age > 26 } # => returns true if more than 1 person is over 26.
 101    def many?(&block)
 102      size = block_given? ? select(&block).size : self.size
 103      size > 1
 104    end
 105 
 106    # Returns true if none of the elements match the given block.
 107    #
 108    #   success = responses.none? {|r| r.status / 100 == 5 }
 109    #
 110    # This is a builtin method in Ruby 1.8.7 and later.
 111    def none?(&block)
 112      !any?(&block)
 113    end unless [].respond_to?(:none?)
 114 
 115    
 116    # The negative of the Enumerable#include?. Returns true if the collection does not include the object.
 117    def exclude?(object)
 118      !include?(object)
 119    end
 120  end