RxJava RxKotlin for iterating a list of observables

RxJava Iterate.kt

class RxJavaIterate{
 
  val users: List<User> = listOf()
  
  //We want to iterate each of these users in the list and perform a function individually in each items
  //One By One
  Observable.from(users)
    .map(i -> {
      //transform users to username string
      //save each i into db
      })
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(item ->{
      }
  
//   If we already have an observables that emits a list
 fun listObserve(someval: List<User>) : Observable<List<User>{
   return Observable.just(someval)
 }
 listObserve.flatMap(Observable::from)
            .subscribe(item -> {
            })
               
//  If we wanna transform all values in one place but emit them one by one on separate thread
 Observable.create(subscriber ->{
   for(user: User in List<User>){
     subscriber.onNext(doSomethingFunction(user))
   }
   subscriber.onCompleted()
 })
}