Accumulate observable array values into single final array

Question

If I have 2 Observable arrays, x$ and y$:

let x = new BehaviorSubject([1,2,3])
let y = new BehaviorSubject([4,5,6])
let x$ = x.asObservable();
let y$ = y.asObservable();

that I'd like to accumulate into a single array of values such that when subscribed to would emit [1,2,3,4,5,6], how can I achieve that?

It depends if you want to wait until they both complete or you want to accumulate values as they arrive. What you expect to happen when you call x.next(7)? — martin
– martin, Commented Mar 27, 2018 at 16:58
I would want them to accumulate as received. I'd expect [1,2,3,4,5,6,7] — Jeremy Thomas
– Jeremy Thomas, Commented Mar 27, 2018 at 17:05
So sometimes you're going to push arrays like x.next([1, 2, 3]) and sometimes individual values like x.next(7)? — martin
– martin, Commented Mar 27, 2018 at 17:08
I see now why this is troublesome. I guess I would have access to the full array of values so I would expect x.next([1,2,3,4]) and y.next([4,5,6,7]) to emit [1,2,3,4,4,5,6,7] — Jeremy Thomas
– Jeremy Thomas, Commented Mar 27, 2018 at 17:10

error · Accepted Answer · 2018-03-27 17:18:56Z

1

Observable.combineLatest( x, y )
.map( ( [ x, y ] ) => ( [ ...x, ...y ] ) );

answered Mar 27, 2018 at 17:18

error

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Comments

martin · Accepted Answer · 2018-03-27 17:13:27Z

1

If it's this simple you can just use scan() to collect all values. It doesn't even matter what's the source so you can just merge the two Observables:

Observable.merge(x, y)
  .scan((acc, arr) => [...acc, ...arr], [])
  .subscribe();

answered Mar 27, 2018 at 17:13

martin

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2 Comments

Jeremy Thomas Over a year ago

your response would be correct if I was appending to the existing array, but since I'm providing the complete array, this results in duplication

martin Over a year ago

so you didn't want to accumulate values as they arrive but rather concat the two most recent values from both Observables :).

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