Generates array of objects grouped by key.

groupBy.ts

const groupBy = <K, V>(arr: readonly V[], getKey: (cur: V, idx: number, src: readonly V[]) => K): V[][] =>
  arr.reduce((acc, cur, idx, src) => {
    const key = getKey(cur, idx, src);
    const item = acc.find(([k,]) => k === key);
    if (item) {
      const [, v] = item;
      v.push(cur);
    } else {
      acc.push([key, [cur]]);
    }
    return acc;
  }, [] as [K, V[]][])
  .map(([, v]) => v);

export default groupBy;