export const groupBy = <T, K extends keyof any>(arr: T[], key: (i: T) => K) =>
  arr.reduce((groups, item) => 
  {
    (groups[key(item)] ||= []).push(item);
    return groups;
  }, {} as Record<K, T[]>);

export function groupByMap<K, V>(list: Array<V>, keyGetter: (input: V) => K): Map<K, Array<V>> 
{
    const map = new Map<K, Array<V>>();
    list.forEach((item) => {
         const key = keyGetter(item);
         const collection = map.get(key);
         if (!collection) {
             map.set(key, [item]);
         } else {
             collection.push(item);
         }
    });
    return map;
}