code: def prepare_sum_row(pattern)
          return if pattern.nil? || pattern.empty?
          @sum_row_pos, sum_row_pattern = pattern.split(/(?<=^top|^eof):/i)
          @sum_row_pos.upcase!
          @sum_row = Hash.new
          @sum_row_patterns = split_by_comma_regex(sum_row_pattern)
        end
docs: Initializes sum_row_pos, sum_row and sum_row_patterns based on the
   provided sum option