# File lib/ai4r/clusterers/single_linkage.rb, line 36
      def initialize
        @distance_function = lambda do |a,b| 
            Ai4r::Data::Proximity.squared_euclidean_distance(
              a.select {|att_a| att_a.is_a? Numeric} , 
              b.select {|att_b| att_b.is_a? Numeric})
          end
      end