https://sifrovacky.cz/assets/stats/helpers/collection-9a0d8306.js

1const group = (result, key, value) => {
2  result[key] ||= [];
3  return result[key].push(value);
4};
5
6export function groupBy(arr, f) {
7  const result = {};
8  for (const x of arr) {
9    group(result, f(x), x);
10  }
11  return result;
12}
13
14const index = (result, key, value) => (result[key] = value);
15export function indexBy(arr, f) {
16  const result = {};
17  for (const x of arr) {
18    index(result, f(x), x);
19  }
20  return result;
21}
22
23export function sortBy(array, getValue) {
24  return [...array].sort((a, b) => {
25    const x = getValue(a);
26    const y = getValue(b);
27
28    if (x < y) return -1;
29    if (x > y) return 1;
30    return 0;
31  });
32}