def missing_values_rows missing_values=[nil]
      number_of_missing = each_row.map do |row|
        row.indexes(*missing_values).size
      end

      Daru::Vector.new number_of_missing, index: @index, name: "#{@name}_missing_rows"
    end
Return a vector with the number of missing values in each row.

== Arguments

* +missing_values+ - An Array of the values that should be
treated as 'missing'. The default missing value is *nil*.