Function groupBy

frontend/src/utils/collections.ts:1–12

(
  array: T[],
  keyOf: (item: T) => K
)

export const groupBy = <T, K>(
  array: T[],
  keyOf: (item: T) => K
): Map<K, T[]> => {
  return array.reduce((map, item) => {
    const key = keyOf(item);
    const list = map.get(key) ?? map.set(key, []).get(key)!;
    list.push(item);

    return map;
  }, new Map<K, T[]>());
};

export const keyBy = <T, K>(array: T[], keyOf: (item: T) => K): Map<K, T> => {
  return array.reduce((map, item) => {