this.studentService.results$
      .pipe(
        // takeUntil(timer$)
        )
      .subscribe(data => {
        if (data && data.length > 0) {
          this.dataSource = new MatTableDataSource(data);
          this.dataSource.paginator = this.paginator;
          this.dataSource.sort = this.sort;
        }
      },
      (error: any) => console.error(error),
      () => console.log('complete')
    );