def row_keys=(val)
      raise ArgumentError, 'Illegal agrument type' unless val.is_a?(Array)
      raise ArgumentError, 'Unmatched size' if val.size < @row_keys.size
      @row_keys = val.map.with_index { |v, i| [v, i] }.to_h
    end
def row_keys=(val)
      raise ArgumentError, 'Illegal agrument type' unless val.is_a?(Array)
      raise ArgumentError, 'Unmatched size' if val.size < @row_keys.size
      @row_keys = val.map.with_index { |v, i| [v, i] }.to_h
    end
Set row keys
 @param val [Array]