type Handler<T> = (val: T) => string | number | boolean | undefined;
/**
 * Return a grouped object from an array.
 * Take Note: This function will automatically filter out any non/empty objects from the array
 *
 * Example:
 *  const group = groupBy([
 *      {tally: 20, name: 'Peter'},
 *      {tally: 40, name: 'Jake'},
 *      {tally: 5, name: 'Bob'},
 *  ], el => el.tally > 15);
 * Output:
 *  {
 *      false: [{tally: 5, name: 'Bob'}],
 *      true: [{tally: 20, name: 'Peter'}, {tally: 40, name: 'Jake'}],
 *  }
 *
 * @param {T[]} val - Array or Set to group
 * @param {Handler<T>|keyof T} handler - String or a function, determines what to group by
 */
declare function groupBy<T extends Record<string, any>>(val: T[] | Set<T>, handler: Handler<T> | keyof T): Record<string, T[]>;
export { groupBy, groupBy as default };