i Need to take one element in result observale-CodePudding

I want to retun only a valure: in html

 <tr *ngFor="let valCorr of valueCall| async">
        <th>{{valCorr }}</th>
    </tr>

in ts

 valueCall:Observable<number[]>
    //this.studentService.getResult() return an Observable<number[]>
     this.valueCall:Observable=this.studentService.getResult().pipe(map(result=> result.filter(x => x>2)),take(1));

in my serivce

 getResult():Observable<number[]> {
    return of([1,2,3,4,5,6]);
  }

the result is not only one element take it seems doesn't work. anyone can help me?

CodePudding user response：

Hi buddy you do that with this approach use find instead of filter to get single value and then convert that single value to type array

this.valueCall = this.getResult().pipe(
  map((result) => {
    let a = result.find((x) => x > 2);
    return [a];
  })
);

CodePudding user response：

take rxjs operator not get one element else only execute one time the observable and unsubscribe, you're looking for

map((result:any[])=> {
  const values=result.filter(x => x>2)
  //be sure there're at least one element else return null
  return values.length?values[0]:null
})

UPDATE: About "take" If we has an observable like

getResult():Observable<number[]> {
    return timer(0,1000); //return 0,1,2,3.... each second
}

If we use pipe(take(1))

getResult().pipe(take(1))

When receive the first value (0) we unsubscribe -no more values are getting-

see a simple stackblitz