# File lib/ai4r/classifiers/hyperpipes.rb, line 30
      def build(data_set)
        data_set.check_not_empty
        @data_set = data_set
        @domains = data_set.build_domains
        
        @pipes = {}
        @domains.last.each {|cat| @pipes[cat] = build_pipe(@data_set)}
        @data_set.data_items.each {|item| update_pipe(@pipes[item.last], item) }
        
        return self
      end