# File lib/ai4r/classifiers/zero_r.rb, line 30
      def build(data_set)
        data_set.check_not_empty
        @data_set = data_set
        frequence = {}
        max_freq = 0
        @class_value = nil
        @data_set.data_items.each do |example|
          class_value = example.last
          class_frequency = frequence[class_value]
          class_frequency = (class_frequency) ? class_frequency+1 : 1
          if max_freq < class_frequency
            max_freq = class_frequency
            @class_value = class_value
          end
        end
        return self
      end