normalize (Gruff::Base)

    # File lib/gruff/base.rb, line 521
        def normalize(force=false)
          if @norm_data.nil? || force
            @norm_data = []
            return unless @has_data

            calculate_spread

            @data.each do |data_row|
              norm_data_points = []
              data_row[DATA_VALUES_INDEX].each do |data_point|
                if data_point.nil?
                  norm_data_points << nil
                else
                  norm_data_points << ((data_point.to_f - @minimum_value.to_f ) / @spread)
                end
              end
              @norm_data << [data_row[DATA_LABEL_INDEX], norm_data_points, data_row[DATA_COLOR_INDEX]]
            end
          end
        end