array.rb

class Array
  def duplicates?(element)
    (self.select {|elem| elem == element}).size > 1 
  end
  def stepwise
    self.each do |element1|
      self.each do |element2|
        next if element1 == element2
        yield element1, element2
      end
    end
  end
  def comparing_collect
    accumulator = [] # collect implementation copied from Rubinius
    stepwise {|element1, element2| accumulator << element1 if yield(element1, element2)}
    accumulator.compact
  end
end