`groupBy` function

220124-organize-object-into-array.js

const o = [
  { name: 'Bobby', group: 1 },
  { name: 'Jimmy', group: 2 },
  { name: 'Tommy', group: 1 },
];

function groupBy(arr, key = 'group') {
  const map = arr.reduce((acc, curr) => ({
    ...acc,
    [curr[key]]: [...(acc[curr[key]] || []), curr],
  }), {});
  return Object.values(map);
}

const z = groupBy(o);

console.log(z);

// [
//   [ { name: 'Bobby', group: 1 }, { name: 'Tommy', group: 1 } ],
//   [ { name: 'Jimmy', group: 2 } ]
// ]