signature: reduce(accumulator: function, seed: any): Observable

Reduces the values from source observable to a single value that's emitted when the source completes.

:bulb: Just like Array.prototype.reduce()

:bulb: If you need the current accumulated value on each emission, try scan!


Example 1: Sum a stream of numbers

( StackBlitz | jsBin | jsFiddle )

import { of } from 'rxjs/observable/of';
import { reduce } from 'rxjs/operators';

const source = of(1, 2, 3, 4);
const example = source.pipe(reduce((acc, val) => acc + val));
//output: Sum: 10'
const subscribe = example.subscribe(val => console.log('Sum:', val));

Additional Resources

:file_folder: Source Code:

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