/** PURE_IMPORTS_START .._operators_groupBy PURE_IMPORTS_END */
import { groupBy as higherOrder, GroupedObservable } from '../operators/groupBy';
export { GroupedObservable };
/* tslint:enable:max-line-length */
/**
 * Groups the items emitted by an Observable according to a specified criterion,
 * and emits these grouped items as `GroupedObservables`, one
 * {@link GroupedObservable} per group.
 *
 * <img src="./img/groupBy.png" width="100%">
 *
 * @example <caption>Group objects by id and return as array</caption>
 * Observable.of<Obj>({id: 1, name: 'aze1'},
 *                    {id: 2, name: 'sf2'},
 *                    {id: 2, name: 'dg2'},
 *                    {id: 1, name: 'erg1'},
 *                    {id: 1, name: 'df1'},
 *                    {id: 2, name: 'sfqfb2'},
 *                    {id: 3, name: 'qfs3'},
 *                    {id: 2, name: 'qsgqsfg2'}
 *     )
 *     .groupBy(p => p.id)
 *     .flatMap( (group$) => group$.reduce((acc, cur) => [...acc, cur], []))
 *     .subscribe(p => console.log(p));
 *
 * // displays:
 * // [ { id: 1, name: 'aze1' },
 * //   { id: 1, name: 'erg1' },
 * //   { id: 1, name: 'df1' } ]
 * //
 * // [ { id: 2, name: 'sf2' },
 * //   { id: 2, name: 'dg2' },
 * //   { id: 2, name: 'sfqfb2' },
 * //   { id: 2, name: 'qsgqsfg2' } ]
 * //
 * // [ { id: 3, name: 'qfs3' } ]
 *
 * @example <caption>Pivot data on the id field</caption>
 * Observable.of<Obj>({id: 1, name: 'aze1'},
 *                    {id: 2, name: 'sf2'},
 *                    {id: 2, name: 'dg2'},
 *                    {id: 1, name: 'erg1'},
 *                    {id: 1, name: 'df1'},
 *                    {id: 2, name: 'sfqfb2'},
 *                    {id: 3, name: 'qfs1'},
 *                    {id: 2, name: 'qsgqsfg2'}
 *                   )
 *     .groupBy(p => p.id, p => p.name)
 *     .flatMap( (group$) => group$.reduce((acc, cur) => [...acc, cur], ["" + group$.key]))
 *     .map(arr => ({'id': parseInt(arr[0]), 'values': arr.slice(1)}))
 *     .subscribe(p => console.log(p));
 *
 * // displays:
 * // { id: 1, values: [ 'aze1', 'erg1', 'df1' ] }
 * // { id: 2, values: [ 'sf2', 'dg2', 'sfqfb2', 'qsgqsfg2' ] }
 * // { id: 3, values: [ 'qfs1' ] }
 *
 * @param {function(value: T): K} keySelector A function that extracts the key
 * for each item.
 * @param {function(value: T): R} [elementSelector] A function that extracts the
 * return element for each item.
 * @param {function(grouped: GroupedObservable<K,R>): Observable<any>} [durationSelector]
 * A function that returns an Observable to determine how long each group should
 * exist.
 * @return {Observable<GroupedObservable<K,R>>} An Observable that emits
 * GroupedObservables, each of which corresponds to a unique key value and each
 * of which emits those items from the source Observable that share that key
 * value.
 * @method groupBy
 * @owner Observable
 */
export function groupBy(keySelector, elementSelector, durationSelector, subjectSelector) {
    return higherOrder(keySelector, elementSelector, durationSelector, subjectSelector)(this);
}
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