Mapping result with rxjs in Angular

Question

I need some help with rxjs in Angular.

I have an API that returns a paginated list of my data from the backend. There data is inside the content attribute of the result. Each entry of the content DOES NOT have an expanded attribute. When I define the interface for the model on the frontend I added that field but now I need to initialize it somehow. This code is working with the for loop but I know it can be done somehow with pipe and map in rxjs.

Cold you suggest how can I do it?

this.service.getData(page, size, id)
    .pipe(
      catchError(() => of([])),
      finalize(() => this.loadingSubject.next(false))
    )
    .subscribe((result: DataPage) => {
      this.dataSubject.next(result.content);
      for(let entry of this.dataSubject.value) {
        entry.expanded = false;
      
      this.totalElementsSubject.next(result.totalElements);
      this.loadingSubject.next(false);
    });