> For the complete documentation index, see [llms.txt](https://www.rxjs.es/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.rxjs.es/operadores/mathematical-aggregate/reduce.md).

# reduce

💡 Si se necesita el valor acumulado en cada emisión, se puede utilizar [scan](https://github.com/puntotech/rxjs-docu/blob/master/operators/transformation/scan/README.md)

<details>

<summary>Signatura</summary>

#### Firma

`reduce<T, R>(accumulator: (acc: T | R, value: T, index?: number) => T | R, seed?: T | R): OperatorFunction<T, T | R>`

#### Parámetros

#### Retorna

`OperatorFunction<T, T | R>`: Un Observable que emite un solo valor, resutante de haber acumulado los valores emitidos por el Observable fuente.

</details>

## Descripción

Combina todos los valores emitidos por la fuente mediante una función acumuladora, que indica cómo unir cada nuevo valor al valor acumulado.

![Diagrama de canicas del operador reduce](https://github.com/puntotech/rxjs-docu/blob/master/doc/operators/mathematical-aggregate/assets/images/marble-diagrams/mathematical-aggregate)

Al igual que `Array.prototype.reduce()`, el operador `reduce` aplica una función acumuladora a cada valor emitido por el Observable fuente para reducirlos a un único valor, que se emite en el Observable resultante. Se debe tener en cuenta que `reduce` solo emite un valor, cuando el Observable fuente se completa. Es equivalente a utilizar el operador `scan` junto al operador `last`.

Retorna un Observable que aplica la función acumuladora especificada a cada elemento emitido por el Observable fuente. Si se especifica un valor `seed`, se utilizará dicho valor como valor inicial para la acumulación inicial. Si no se especificara un valor inicial, se utilizará el primer elemento de la fuente como tal.

## Ejemplos

### Ejemplos de la documentación oficial

**Contar el número de eventos click que ocurran en 5 segundos**

```javascript
import { fromEvent, interval } from "rxjs";
import { reduce, takeUntil, mapTo } from "rxjs/operators";

const clicksInFiveSeconds = fromEvent(document, "click").pipe(
  takeUntil(interval(5000))
);
const ones = clicksInFiveSeconds.pipe(mapTo(1));
const seed = 0;
const count = ones.pipe(reduce((acc, one) => acc + one, seed));
count.subscribe((x) => console.log(x));
```

<details>

<summary>Sobrecargas</summary>

#### Firma

`reduce(accumulator: (acc: R, value: T, index: number) => R, seed: R): OperatorFunction<T, R>`

#### Parámetros

#### Retorna

`OperatorFunction<T, R>`

#### Firma

`reduce(accumulator: (acc: T, value: T, index: number) => T, seed?: T): MonoTypeOperatorFunction<T>`

#### Parámetros

#### Retorna

`MonoTypeOperatorFunction<T>`

#### Firma

`reduce(accumulator: (acc: R, value: T, index: number) => R): OperatorFunction<T, R>`

#### Parámetros

#### Retorna

`OperatorFunction<T, R>`

</details>

### Recursos adicionales

[![Source code](https://github.com/puntotech/rxjs-docu/blob/master/doc/operators/mathematical-aggregate/assets/icons/source-code.png)](https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/reduce.ts)

[Documentación oficial en inglés](https://rxjs.dev/api/operators/reduce)


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