CODEWITHSUNDEEP
angulardictionaryrxjs
Patrick P.
Patrick P.

Reputation: 109

How to filter a RxJS Map Oberservable

i am currently struggeling by filtering a Map Observable with RxJS. What i try to do is to do reduce my Map-Object by a filter function before subscribing to it.

I init the Subject like this:

public myObjects: ReplaySubject<Map<number, MyClass>> = new ReplaySubject<Map<number, MyClass>>(1);

And that's how I try to filter:

public subscribeToIncomingObjects() {
this.myObjects.map( (currentValue:Map<number, MyObject>) => Array.from(currentValue.values())).filter(
  (con:myObject, index) => {
    return someCondition;
  }
);
 }

For some reason con is of type Array and not a single instance. I would really appreciate any advise.

Upvotes: 2

Views: 763

Answers (1)

n00dl3
n00dl3

Reputation: 21564

First things first,

You are dealing with an Observable :

this.myObjects.map( (currentValue:Map<number, MyObject>) => Array.from(currentValue.values()))

returns an Observable<MyObject[]>. So if you call .filter() on that Observable, you are filtering Observable's broadcast.

You could just call your filter like this :

public subscribeToIncomingObjects() {
  this.myObjects.map((currentValue: Map < number, MyObject > ) => {
    return Array.from(currentValue.values())
      .filter((con: myObject, index) => someCondition);
  });
}

BUT you would still get an array, if you need a single instance you'd better use Array.prototype.find() if it is available :

public subscribeToIncomingObjects() {
  this.myObjects.map((currentValue: Map < number, MyObject > ) => {
    return Array.from(currentValue.values())
      .find((con: myObject, index) => someCondition);
  });
}

or, still using Array.prototype.filter():

public subscribeToIncomingObjects() {
  this.myObjects.map((currentValue: Map < number, MyObject > ) => {
    return Array.from(currentValue.values())
      .filter((con: myObject, index) => someCondition)[0];
  });
}

Upvotes: 1

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