var csv = require('Text::CSV').new(
    Hash(eol => "\n")
);

# Open
var csvfile = %f'data.csv';
var fh = csvfile.open_r;

# Read
var rows = [];
var header = csv.getline(fh);
while (var row = csv.getline(fh)) {
    rows.append(row.map{.to_num});
}

# Process
header.append('SUM');
rows.each { |row| row.append(row.sum) };

# Write
var out = csvfile.open_w;
[header, rows...].each { |row|
    csv.print(out, row);
};