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/** PURE_IMPORTS_START .._operators_count PURE_IMPORTS_END */
import { count as higherOrder } from '../operators/count';
/**
* Counts the number of emissions on the source and emits that number when the
* source completes.
*
* <span class="informal">Tells how many values were emitted, when the source
* completes.</span>
*
* <img src="./img/count.png" width="100%">
*
* `count` transforms an Observable that emits values into an Observable that
* emits a single value that represents the number of values emitted by the
* source Observable. If the source Observable terminates with an error, `count`
* will pass this error notification along without emitting a value first. If
* the source Observable does not terminate at all, `count` will neither emit
* a value nor terminate. This operator takes an optional `predicate` function
* as argument, in which case the output emission will represent the number of
* source values that matched `true` with the `predicate`.
*
* @example <caption>Counts how many seconds have passed before the first click happened</caption>
* var seconds = Rx.Observable.interval(1000);
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var secondsBeforeClick = seconds.takeUntil(clicks);
* var result = secondsBeforeClick.count();
* result.subscribe(x => console.log(x));
*
* @example <caption>Counts how many odd numbers are there between 1 and 7</caption>
* var numbers = Rx.Observable.range(1, 7);
* var result = numbers.count(i => i % 2 === 1);
* result.subscribe(x => console.log(x));
*
* // Results in:
* // 4
*
* @see {@link max}
* @see {@link min}
* @see {@link reduce}
*
* @param {function(value: T, i: number, source: Observable<T>): boolean} [predicate] A
* boolean function to select what values are to be counted. It is provided with
* arguments of:
* - `value`: the value from the source Observable.
* - `index`: the (zero-based) "index" of the value from the source Observable.
* - `source`: the source Observable instance itself.
* @return {Observable} An Observable of one number that represents the count as
* described above.
* @method count
* @owner Observable
*/
export function count(predicate) {
return higherOrder(predicate)(this);
}
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