I want to change output of API with rxjs

I have API call, where I use pipe

getCountriesListNights(){
    const r = this.http.get<any>(this.APIUrl + "/WorldMapDataNights?&year=" + this.selectedYear + "&month=" + this.selectedMonth +"&gender=" + this.selectedGender + "&age="+this.selectedAge + "&quarter=" + this.selectedQuarter).pipe(map((res) => {return res.map((res: { id: any; countryName: any; value: any; year: any; name: string; multiPolygon: any[] }) =>({countryName: res.countryName,  id: res.id,  value: res.value, year: res.year, name: res.name, multiPolygon: res.multiPolygon  }))})).subscribe(res =>{
      this.renderMapObject(res);
    });
  };

It works good, I can change the output, but I want to divide value by other API’s value, when country name’s are same in both API’s. (I want to divide res.value by otherapi.value.)

what can I do now?