Transform the array of objects returned as Observable

Question

There is small correction. What we are returning is Object[] and not Object. The method signature is also changed as below - I have a method which returns Observable as below-

 getData(url: string): Observable<Object[]> {

    return this.http.get<Object[]>(url);
  }

Where the Object is like below :

{

  property1 : value1 
  property2 : value2 
  property3 : "" // no value right now 
}

What I want to do is :

return Observable<Object[]> (Please note same object)

Where the Object is like below :

{

  property1 : value1 
  property2 : value2 
  property3 : value1 + value2; //combine property1 and property2 values 
}

How can we achieve this ?

I know we have to use rxjs map operator but how do we use it ?

The url Transforming Observable with .map talks about transforming Array but not Map

How can we achieve this using Map operator on Observable ?

.map(obj => ({...obj, property3: obj[property1] + obj[property2]}) — Julius Dzidzevičius
– Julius Dzidzevičius, Commented Nov 20, 2019 at 5:56
Your method signature is not TypeScript, looks more like C# or Java, so this can't be valid Angular code. What problem do you have with returning the object as you described? — Markus Dresch
– Markus Dresch, Commented Nov 20, 2019 at 5:57

Nimer Awad · Accepted Answer · 2019-11-20 06:33:51Z

1

Okay, you need to map data of Observable before it's been subscribed.

There's a function called pipe that used to modify data of Observable and returns an Observable.

For your case:

Observable<Object> getData(){
    // let assume your observable is called getObs
    return getObs.pipe(
        map(objs => objs.map(obj => {
            obj[property3] = obj[property1] + obj[property2]);
            return objs;
        })
        )
    )
}

Btw, all rxjs/operators must be called inside pipe function, not just map.

edited Nov 20, 2019 at 6:33

answered Nov 20, 2019 at 6:00

Nimer Awad

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1 Comment

Nimer Awad Over a year ago

Okay, check it now

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