def wss(objects = nil)
      if objects.nil?
        objects = @objects.map { |x| Array.new(x[1], x[0]) }.flatten
      end

      cluster_mean = mean
      ss = 0
      objects.each do |object|
        ss += (cluster_mean - object) * (cluster_mean - object)
      end
      ss
    end
def wss(objects = nil)
      if objects.nil?
        objects = @objects.map { |x| Array.new(x[1], x[0]) }.flatten
      end

      cluster_mean = mean
      ss = 0
      objects.each do |object|
        ss += (cluster_mean - object) * (cluster_mean - object)
      end
      ss
    end
Returns within cluster sum of squares