split_tournament.rb

# encoding: UTF-8
module Machine::Nudge
  class SplitTournament < Machine
    
    def process (answers)
      
      @criteria ||= []
      @tournament_size ||= 20
      winners = []
      losers = []
      
      until answers.empty?
        answers.shuffle!
        some = answers.slice!(0..@tournament_size)
        
        indices_of_best = []

        some.each_with_index do |a, index|
          nondominated = true

          some.each do |b|
            nondominated_vs_b = true

            @criteria.each do |score_name|
              a_score = a.score(score_name)
              b_score = b.score(score_name)

              if a_score < b_score
                nondominated_vs_b = true
                break
              elsif nondominated_vs_b
                nondominated_vs_b &&= (a_score == b_score)
              end
            end

            break unless nondominated &&= nondominated_vs_b
          end

          indices_of_best << index if nondominated
        end

        indices_of_best.reverse.each do |i|
          winners << some.delete_at(i)
        end
        
        left = some.length
        left.times {losers << some.pop}
      end

      return :winners => winners,
             :losers => losers
    end
  end
end