Best way to "flatten" an array inside an RxJS Observable
Solution 1
Actually if you need it inside the stream just use this:
.flatMap(items => of(...items))
Solution 2
If it is a synchronous operation, I would suggest to use javascript's Array.map
instead, it even should save you some performance:
const dataFromBackend = Rx.Observable.of([
{ name: 'item1', active: true },
{ name: 'item2', active: false },
{ name: 'item3', active: true }
]);
dataFromBackend
.map(items => items.map(item => item.name))
.subscribe();
AngularChef
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Updated on May 14, 2020Comments
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AngularChef about 4 years
My backend frequently returns data as an array inside an RxJS 5 Observable (I'm using Angular 2).
I often find myself wanting to process the array items individually with RxJS operators and I do so with the following code (JSBin):
const dataFromBackend = Rx.Observable.of([ { name: 'item1', active: true }, { name: 'item2', active: false }, { name: 'item3', active: true } ]); dataFromBackend // At this point, the obs emits a SINGLE array of items .do(items => console.log(items)) // I flatten the array so that the obs emits each item INDIVIDUALLY .mergeMap(val => val) // At this point, the obs emits each item individually .do(item => console.log(item)) // I can keep transforming each item using RxJS operators. // Most likely, I will project the item into another obs with mergeMap() .map(item => item.name) // When I'm done transforming the items, I gather them in a single array again .toArray() .subscribe();
The
mergeMap(val => val)
line doesn't feel very idiomatic.Is there a better way to apply transformations to the members of an array that's emitted by an Observable?
NB. I want RxJS operators (vs array methods) to transform my items because I need the ability to project each item into a second observable. Typical use case: backend returns of list of item ids and I need to request all of these items from the backend.