module Enumerable #:nodoc: # Collect an enumerable into sets, grouped by the result of a block. Useful, # for example, for grouping records by date. # # e.g. # # latest_transcripts.group_by(&:day).each do |day, transcripts| # p "#{day} -> #{transcripts.map(&:class) * ', '}" # 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" def group_by inject({}) do |groups, element| (groups[yield(element)] ||= []) << element groups end end # Calculates a sum from the elements. Examples: # # payments.sum { |p| p.price * p.tax_rate } # payments.sum(&:price) # # This is instead of payments.inject { |sum, p| sum + p.price } # # Also calculates sums without the use of a block: # [5, 15, 10].sum # => 30 # # The default identity (sum of an empty list) is zero. # However, you can override this default: # # [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0) # def sum(identity = 0, &block) return identity unless size > 0 if block_given? map(&block).sum else inject { |sum, element| sum + element } end end # Convert an enumerable to a hash. Examples: # # people.index_by(&:login) # => { "nextangle" => , "chade-" => , ...} # people.index_by { |person| "#{person.first_name} #{person.last_name}" } # => { "Chade- Fowlersburg-e" => , "David Heinemeier Hansson" => , ...} # def index_by inject({}) do |accum, elem| accum[yield(elem)] = elem accum end end end