# File lib/ai4r/classifiers/one_r.rb, line 30
      def build(data_set)
        data_set.check_not_empty
        @data_set = data_set
        if (data_set.num_attributes == 1) 
          @zero_r = ZeroR.new.build(data_set)
          return self;
        else
          @zero_r = nil;
        end
        domains = @data_set.build_domains
        @rule = nil
        domains[1...-1].each_index do |attr_index|
          rule = build_rule(@data_set.data_items, attr_index, domains)
          @rule = rule if !@rule || rule[:correct] > @rule[:correct]
        end
        return self
      end