import { IEnumerable } from '../enumerable';
import { IEqualityComparer } from '../equality-comparer';
import { IGrouping } from '../grouping';
export declare function groupBy<TSource, TKey, TElement = TSource>(source: Iterable<TSource>, keySelector: (item: TSource) => TKey, elementSelector?: (item: TSource) => TElement, comparer?: IEqualityComparer<TKey>): IEnumerable<IGrouping<TKey, TElement>>;