Concat multilevel API calls in Angular using rxjs

I am new to rxjs I am calling three api calls using the hacker new api. I want to concat response of the last api call to the second api call.

I want to achieve something like this.

[
    {
        "by": "john"
        "title": "Sample title"
        "time":1657786985
        "karma": 123456 // this is from the third api call that i want to merge
    },
    {
        "by": "jane"
        "title": "Sample title 2"
        "time":1657786333
        "karma": 123456 // this is from the third api call that i want to merge
    }
]

So far this is my code

this.service.fetchStories().pipe( // get list of id array
      switchMap(idArray => forkJoin(
        idArray.map(id => this.service.fetchStoryItems(id).pipe( // first api call
          concatMap(itm => this.service.fetchUserById(itm.by)) // second api call i want to merge { karma } to the first api call
        )))
      ),
      take(1)
    ).subscribe(data => console.log(data));

But the result is I am getting only the response of the last api call. Can somebody help me. I am trying to learn rxjs.

>Solution :

All you need to do is to pipe the third call again and merge the results.

this.service.fetchStories().pipe( // get list of id array
      switchMap(idArray => forkJoin(
        idArray.map(id => this.service.fetchStoryItems(id).pipe( // first api call
          concatMap(itm => this.service.fetchUserById(itm.by).pipe(map(({karma}) => ({ ...itm, karma }))))
        )))
      ),
      take(1)
    ).subscribe(data => console.log(data));