import {Subject} from "rxjs/Subject";
        import 'rxjs/add/operator/distinctUntilChanged';

        const sub: Subject<number> = new Subject<number>();

        sub.distinctUntilChanged().subscribe((val: number) => {
            console.log(val);
        });

        sub.next(0);
        sub.next(0);
        sub.next(1);
        sub.next(2);
        sub.next(2);
        sub.next(2);
        sub.next(3);

        // will output 0,1,2,3