title: Order network requests result with RxSwift
body: <p>I currently have a set of network requests to fire.
  The problem is that I need to order the results of them to fit the order I fired them.</p>
  
  <p>My current code is the following:</p>
  
  <pre><code>for url in config.fieldImages.map ({ URL(string: $0)! }) {
      self.getWheelFieldImage(url: url)
          .takeUntil(.inclusive, predicate: { (_) -&gt; Bool in
              images.count == config.fieldImages.count - 1
          })
          .subscribe(onNext: { (anImage) in
              images.append(anImage)
          }, onError: { (error) in
              completion(nil, nil, error)
          }, onCompleted: {
              completion(images, false, nil)
              self.lastUpdate = Date()
          }, onDisposed: {
      })
      .disposed(by: self.disposeBag)
  }
  </code></pre>
  
  <p><strong>I'm wondering if there is an easy way to order these results in the same order I fired them, using RxSwift</strong>.</p>
  
  <p>EDIT:</p>
  
  <p>I try to explain the problem better. I have this array with N URLs and I fire the requests one after the other (1,2,3,4...).</p>
  
  <p>I need to have back the result from these requests in the same order (R1, R2, R3, R4, where R1 is the response from request 1 etc...) to store the images in the resulting array.</p>
  
  <p>I can wait all to finish. No problem.</p>