title: RxSwift - How to concatenate observables of collection
body: <p>I'm trying to concatenate two observables of collection with <code>concat()</code> operator, however, it's not working as expected.</p>
  
  <p>I've two observables:</p>
  
  <pre><code>let first = Observable&lt;[Int]&gt;.create { observer in
      observer.onNext([1, 2])
      observer.onCompleted()
      return Disposables.create()
  }
  
  let second = PublishSubject&lt;[Int]&gt;()
  </code></pre>
  
  <p>Using <code>concat()</code>:</p>
  
  <pre><code>let items = Observable.concat([first, second])
  
  items.subscribe(onNext: {
      print($0)
  })
  
  second.onNext([3, 4, 5])
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>[1, 2]
  [3, 4, 5]
  </code></pre>
  
  <p>What I want:</p>
  
  <pre><code>[1, 2]
  [1, 2, 3, 4, 5]
  </code></pre>