# File lib/ai4r/classifiers/one_r.rb, line 84
      def build_rule(data_examples, attr_index, domains)
        domain = domains[attr_index]
        value_freq = Hash.new
        domain.each do |attr_value| 
          value_freq[attr_value] = Hash.new { |hash, key| hash[key] = 0 }
        end
        data_examples.each do |data|
          value_freq[data[attr_index]][data.last] = value_freq[data[attr_index]][data.last] + 1
        end
        rule = {}
        correct_instances = 0
        value_freq.each_pair do |attr, class_freq_hash|  
          max_freq = 0
          class_freq_hash.each_pair do |class_value, freq| 
            if max_freq < freq
              rule[attr] = class_value 
              max_freq = freq
            end
          end
          correct_instances += max_freq
        end
        return {:attr_index => attr_index, :rule => rule, :correct => correct_instances}
      end