# File lib/core/facets/enumerable/commonality.rb, line 17 def commonality( &block ) had_no_block = !block block ||= lambda { |item| item } result = Hash.new { |hash, key| hash[key] = Array.new } self.each do |item| key = block.call(item) result[key] << item end result.reject! do |key, values| values.size <= 1 end #return had_no_block ? result.values.flatten : result return result end