https://www.youtube.com/watch?v=1DMolJ2FrNY

es6-map-reduce.js

import fs from 'fs'

var output = fs.readFileSync('input.txt', 'utf8')
    .trim()     // remove end of line
    .split('\n')
    .map(line => line.split('\t'))
    .reduce((customers, [ user, name, price, quality ]) => {
        customers[user] = customers[user] || [];
        customers[user].push({ name, price, quality });
        return customers;
    }, {});

console.log(JSON.stringify(output, null, 2));

input.txt

mark johansson	waffle iron	80	2
mark johansson	blender	200	1
mark johansson	knife	10	4
Nikita Smith	waffle iron	80	1
Nikita Smith	knife	10	2
Nikita Smith	pot	20	3