import { from } from 'rxjs';
import { groupBy, mergeMap, toArray } from 'rxjs/operators';
{ name: 'Sue', age: 25 },
{ name: 'Joe', age: 30 },
{ name: 'Frank', age: 25 },
{ name: 'Sarah', age: 35 }
const source = from(people);
const example = source.pipe(
groupBy(person => person.age),
// return each item in group as array
mergeMap(group => group.pipe(toArray()))
[{age: 25, name: "Sue"},{age: 25, name: "Frank"}]
[{age: 35, name: "Sarah"}]
const subscribe = example.subscribe(val => console.log(val));