Rxswift map + concat in parallel

This Observable is executing the following

• Given a source observable


• we use map to perform some async work


• we use concat to return the result of the async work in order

The following is returning the desired result, but I would like to start
the async work in parallel.

What the correct way of doing it with Rx?

import RxSwift



func delay(time: Int, closure: () -> Void) {

  dispatch_after(

    dispatch_time(DISPATCH_TIME_NOW, Int64(time * Int(NSEC_PER_SEC))),

    dispatch_get_main_queue(), closure)

}



func doAsyncWork(value: Int, desc: String, time: Int) -> Observable<Int> {

  return Observable.create() { (observer) -> Disposable in

    print(desc)

    delay(time) {

      observer.onNext(value)

      observer.onCompleted()

    }

    return NopDisposable.instance

  }

}



let seq = Observable

  .of(1, 2, 3, 4, 5)

  .map { (n) -> Observable<Int> in

    return doAsyncWork(n,

      desc: "start \(n) - wait \(5 - n)",

      time: 6 - n

    )

  }

  .concat()



let sharedSeq = seq.shareReplay(0)

sharedSeq.subscribeNext { print("=> \($0)") }

sharedSeq.subscribeCompleted { print("=> completed") }

This produce

//start 1 - wait 4

// => 1

//start 2 - wait 3

// => 2

//start 3 - wait 2

// => 3

//start 4 - wait 1

// => 4

//start 5 - wait 0

// => 5

The desired output would be

//start 1 - wait 4

//start 2 - wait 3

//start 3 - wait 2

//start 4 - wait 1

//start 5 - wait 0

// => 1

// => 2

// => 3

// => 4

// => 5