Distinct Until Changed

Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item.

Example

A simple example with numbers

content_copyopen_in_newimport { of } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

of(1, 1, 2, 2, 2, 1, 1, 2, 3, 3, 4).pipe(
    distinctUntilChanged(),
  )
  .subscribe(x => console.log(x)); // 1, 2, 1, 2, 3, 4

An example using a compare function

import { of } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';
 
interface Person {
   age: number,
   name: string
}
 
of<Person>(
    { age: 4, name: 'Foo'},
    { age: 7, name: 'Bar'},
    { age: 5, name: 'Foo'},
    { age: 6, name: 'Foo'},
  ).pipe(
    distinctUntilChanged((p: Person, q: Person) => p.name === q.name),
  )
  .subscribe(x => console.log(x));
 
// displays:
// { age: 4, name: 'Foo' }
// { age: 7, name: 'Bar' }
// { age: 5, name: 'Foo' }

import { from } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

const sampleObject = { name: 'Test' };

// Objects must be same reference
const source$ = from([sampleObject, sampleObject, sampleObject]);

// only emit distinct objects, based on last emitted value
source$
  .pipe(distinctUntilChanged())
  .subscribe(console.log);
  // output: {name: 'Test'}