import { scan } from './scan'; import { takeLast } from './takeLast'; import { defaultIfEmpty } from './defaultIfEmpty'; import { pipe } from '../util/pipe'; /* tslint:enable:max-line-length */ /** * Applies an accumulator function over the source Observable, and returns the * accumulated result when the source completes, given an optional seed value. * * Combines together all values emitted on the source, * using an accumulator function that knows how to join a new source value into * the accumulation from the past. * * * * Like * [Array.prototype.reduce()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce), * `reduce` applies an `accumulator` function against an accumulation and each * value of the source Observable (from the past) to reduce it to a single * value, emitted on the output Observable. Note that `reduce` will only emit * one value, only when the source Observable completes. It is equivalent to * applying operator {@link scan} followed by operator {@link last}. * * Returns an Observable that applies a specified `accumulator` function to each * item emitted by the source Observable. If a `seed` value is specified, then * that value will be used as the initial value for the accumulator. If no seed * value is specified, the first item of the source is used as the seed. * * @example Count the number of click events that happened in 5 seconds * var clicksInFiveSeconds = Rx.Observable.fromEvent(document, 'click') * .takeUntil(Rx.Observable.interval(5000)); * var ones = clicksInFiveSeconds.mapTo(1); * var seed = 0; * var count = ones.reduce((acc, one) => acc + one, seed); * count.subscribe(x => console.log(x)); * * @see {@link count} * @see {@link expand} * @see {@link mergeScan} * @see {@link scan} * * @param {function(acc: R, value: T, index: number): R} accumulator The accumulator function * called on each source value. * @param {R} [seed] The initial accumulation value. * @return {Observable} An Observable that emits a single value that is the * result of accumulating the values emitted by the source Observable. * @method reduce * @owner Observable */ export function reduce(accumulator, seed) { // providing a seed of `undefined` *should* be valid and trigger // hasSeed! so don't use `seed !== undefined` checks! // For this reason, we have to check it here at the original call site // otherwise inside Operator/Subscriber we won't know if `undefined` // means they didn't provide anything or if they literally provided `undefined` if (arguments.length >= 2) { return function reduceOperatorFunctionWithSeed(source) { return pipe(scan(accumulator, seed), takeLast(1), defaultIfEmpty(seed))(source); }; } return function reduceOperatorFunction(source) { return pipe(scan((acc, value, index) => { return accumulator(acc, value, index + 1); }), takeLast(1))(source); }; } //# sourceMappingURL=reduce.js.map