/** Selector function to determine the value of a group key */
export declare type GroupBySelectorFn<T> = (obj: T) => any;
/**
 * The "multi" result of a {@link groupBy} call. Describes an array holding exactly 2 values. The first value stores
 * the accumulation result of the main grouping mechanism inside a plain object the second value preserves any
 * foreign values that could be associated with a group
 */
export declare type GroupByResult<T, K extends string> = [
    /** Holds all values that could be associated with a group under their respective {@link GroupBySelectorFn} keys */
    Record<K, T[]>,
    /** Holds all foreign values that couldn't be associated with any group */
    T[]
];
/**
 * Groups the values of an {@link Iterable} into a {@link Record} of respective {@link GroupBySelectorFn} key results,
 * while preserving any non associated value in an {@link Array} of foreign values
 *
 * @param iterable The {@link Iterable} values that should be grouped by their respective keys
 * @param groupBySelectorFn The selector function that should resolve the desired group key values
 */
export declare function groupBy<T, K extends string = string>(iterable: Iterable<T>, groupBySelectorFn: GroupBySelectorFn<T>): GroupByResult<T, K>;