groupBy

signature: groupBy(keySelector: Function, elementSelector: Function): Observable

Group into observables based on provided value.

Examples

Example 1: Group by property

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { from } from 'rxjs';
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