# File lib/ai4r/data/statistics.rb, line 45
      def self.mode(data_set, attribute)
        index = data_set.get_index(attribute)
        count = Hash.new {0}
        max_count = 0
        mode = nil
        data_set.data_items.each do |data_item| 
          attr_value = data_item[index]
          attr_count = (count[attr_value] += 1)
          if attr_count > max_count
            mode = attr_value
            max_count = attr_count
          end
        end
        return mode
      end