def get_maximum_by_stack
      # Get sum of each stack
      max_hash = {}
      @data.each do |data_set|
        data_set[DATA_VALUES_INDEX].each_with_index do |data_point, i|
          max_hash[i] = 0.0 unless max_hash[i]
          max_hash[i] += data_point.to_f
        end
      end

      # @maximum_value = 0
      max_hash.keys.each do |key|
        @maximum_value = max_hash[key] if max_hash[key] > @maximum_value
      end
      @minimum_value = 0
    end
def get_maximum_by_stack
      # Get sum of each stack
      max_hash = {}
      @data.each do |data_set|
        data_set[DATA_VALUES_INDEX].each_with_index do |data_point, i|
          max_hash[i] = 0.0 unless max_hash[i]
          max_hash[i] += data_point.to_f
        end
      end

      # @maximum_value = 0
      max_hash.keys.each do |key|
        @maximum_value = max_hash[key] if max_hash[key] > @maximum_value
      end
      @minimum_value = 0
    end
Used by StackedBar and child classes.

 May need to be moved to the StackedBar class.