arrayToServiceToArray.js

const serviceValues = [ 2, 3, 4 ];
// convert values array into a stream of individual values: Obs[...num]
return Observable.of(serviceValues)
  // call service on each value and get Observable in return: Obs[Obs[newValFromService]]
  .map(val => serviceApi(val))
  // convert stream of observables into a stream of a single array of observables Obs[ [Obs[newVal]] ]
  .toArray()
  // trigger all the service calls with maximum concurrenct
  .switchMap((serviceCalls) => Observable.combineLatest(serviceCalls))
  .subscribe(newVals => console.log('new values from server: ', newVals)) // [...{id: 2, ...data}, {id: 3, ...dat}]