/**
 * Groups an array of objects by the specified key.
 *
 * @example
 * const input = [
 *   { id: 1, category: 'a' },
 *   { id: 2, category: 'a' },
 *   { id: 3, category: 'b' },
 * ];
 *
 * const result = groupBy(input, 'category');
 * // result will be { a: [{ id: 1 }, { id: 2 }], b: [{ id: 3 }] }
 */
export declare function groupBy<T extends Record<string, any>, K extends keyof T>(array: T[], key: K): Record<T[K], T[]>;