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'}
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