# File lib/ai4r/classifiers/prism.rb, line 135
      def build_freq_table(rule_instances, attributes, class_value)
        freq_table = Hash.new()
        rule_instances.each do |data|
          attributes.each do |attr_label|
            attr_freqs = freq_table[attr_label] || Hash.new([0, 0])
            pt = attr_freqs[get_attr_value(data, attr_label)]
            pt = [(data.last == class_value) ? pt[0]+1 : pt[0], pt[1]+1]
            attr_freqs[get_attr_value(data, attr_label)] = pt
            freq_table[attr_label] = attr_freqs
          end
        end
        return freq_table
      end