Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item.
distinctUntilChanged<T, K>(compare?: (x: K, y: K) => boolean, keySelector?: (x: T) => K): MonoTypeOperatorFunction<T>
Parameters
| compare |
Optional. Default is undefined.
Optional comparison function called to test if an item is distinct from the previous item in the source.
|
| keySelector |
Optional. Default is undefined.
Type: (x: T) => K.
|
Returns
MonoTypeOperatorFunction<T>: An Observable that emits items from the source Observable with distinct values.
Description
If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
If a comparator function is not provided, an equality check is used by default.
Example
A simple example with numbers
import { 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' }