signature: groupBy(keySelector: Function, elementSelector: Function): Observable
Group into observables based on provided value.
// 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));
// RxJS v6+
import { from, of, zip } 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 }
];
from(people)
.pipe(
groupBy(
person => person.age,
p => p.name
),
mergeMap(group => zip(of(group.key), group.pipe(toArray())))
)
.subscribe(console.log);
/*
output:
[25, ["Sue", "Frank"]]
[30, ["Joe"]]
[35, ["Sarah"]]
*/
