import { Enumerable } from '../enumerable';
import { Grouping } from '../grouping';
declare module '../enumerable' {
    interface Enumerable<TSource> {
        groupBy<TKey, TElement>(keySelector: (item: TSource) => TKey, elementSelector?: (item: TSource) => TElement): Enumerable<Grouping<TKey, TElement>>;
    }
}
export declare function groupBy<TSource, TKey, TElement>(this: Enumerable<TSource>, keySelector: (item: TSource) => TKey, elementSelector?: (item: TSource) => TElement): Enumerable<Grouping<TKey, TElement>>;