groupBy
signature: groupBy(keySelector: Function, elementSelector: Function): Observable
Group into observables based on provided value.
Examples
Example 1: Group by property
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import { from } from 'rxjs/observable/from';
import { groupBy, mergeMap, toArray } from 'rxjs/operators';
const people = [
{ name: 'Sue', age: 25 },
{ name: 'Joe', age: 30 },
{ name: 'Frank', age: 25 },
{ name: 'Sarah', age: 35 }
];
//emit each person
const source = from(people);
//group by age
const example = source.pipe(
groupBy(person => person.age),
// return each item in group as array
mergeMap(group => group.pipe(toArray()))
);
/*
output:
[{age: 25, name: "Sue"},{age: 25, name: "Frank"}]
[{age: 30, name: "Joe"}]
[{age: 35, name: "Sarah"}]
*/
const subscribe = example.subscribe(val => console.log(val));
Additional Resources
- groupBy
- Official docs - Group higher order observables with RxJS groupBy
- André Staltz - Use groupBy in real RxJS applications
- André Staltz
Source Code:
https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/groupBy.ts