/**
 * Returns an object that groups the iterable of the iterable object into arrays, using the return value of the callback function as the key.
 * @param iterable An iterable object
 * @param callbackfn A function that accepts up to two arguments. The map method calls the callbackfn function one time for each element in `iterable`.
 */
declare function groupBy<T, K extends PropertyKey>(
    iterable: Iterable<T>,
    callbackfn: (value: T, index: number) => K,
): Record<K, T[]>;

/**
 * Returns an object that groups the iterable of the iterable object into arrays, using the return value of the callback function as the key.
 * @param iterable An iterable object
 * @param callbackfn A function that accepts up to two arguments. The map method calls the callbackfn function one time for each element in `iterable`.
 */
declare function groupBy(
    iterable: Iterable<unknown>,
    callbackfn: (value: unknown, index: number) => PropertyKey,
): Record<PropertyKey, unknown[]>;

export = groupBy;