将数组的可观察对象转换为可观察对象的数组

Question

I am trying to convert from an observable of an array:

of([1, 2, 3]);

Into an array of observables:

[ of(1), of(2), of(3) ]

But I am out of ideas. I have tried the following:

of([1, 2, 3]).pipe(map((elements: number[]) => elements.map(element => of(element)))

But this gives me something like this, with an outer observable that I do not desire.

of([ of(1), of(2), of(3) ])

As I want to join the result with other arrays, it is not convenient for me to just subscribe to the outer observable in order to get the array... I think I need an opposite operator of concatAll . Any ideas?

Answer 1

If you know that the observable is always going to be totally synchronous (but keep in mind this is not really something you can check at runtime), you can do this:

const extractValue = <T>(source$: Observable<T[]>): Observable<T>[] => {
  let result: Observable<T>[];
  source$
    .pipe(
      map((arr) => arr.map((value) => of(value))),
      take(1)
    )
    .subscribe((_result) => {
      result = _result;
    });
  return result;
};

Otherwise, you must use an async function:

const extractValue = <T>(
  source$: Observable<T[]>
): Promise<Observable<T>[]> => {
  return source$
    .pipe(
      map((arr) => arr.map((value) => of(value))),
      take(1)
    )
    .toPromise();
};

Answer 2

RxJS#from

from([1,2,3,4,5]).subscribe(console.log) // 1 2 3 4 5

or as a pipable operator

of([1,2,3,4,5]).pipe(
  concatMap(v => from(v))
).subscribe(console.log) // 1 2 3 4 5

Combine that with your transformation

of([1,2,3,4,5]).pipe(
  map((elements: number[]) => 
    elements.map(element => of(element))
  ),
  concatMap(x => from(x))
)

combined

of([1,2,3,4,5]).pipe(
  concatMap((elements: number[]) => 
    from(elements.map(element => of(element)))
  )
)

Answer 3

Maybe you can try to create an Observable from an array and than turn each member in to an Observable using of() function:

const arr = [1, 2, 3];

from(arr).pipe(
  mergeMap((a) => of(a))
);

After that you can handle each observable as you please.