def object_summary
      nval = count_values(*Daru::MISSING_VALUES)
      summary = "\n  factors: #{factors.to_a.join(',')}" \
                "\n  mode: #{mode.to_a.join(',')}" \
                "\n  Distribution\n"

      data = frequencies.sort.each_with_index.map do |v, k|
        [k, v, '%0.2f%%' % ((nval.zero? ? 1 : v.quo(nval))*100)]
      end

      summary + Formatters::Table.format(data)
    end
Displays summary for an object type Vector
@return [String] String containing object vector summary