title: Convert [Observable<T>] to Observable<[T]> in RxSwift
body: <p>Here's my implementation. </p>
  
  <p>I have <code>favCitiesID = Observable&lt;[Int]&gt;</code> that will be flatMap and map. Each city id will be used in API call that will return <code>Observable&lt;CityMappable&gt;</code>. I have reached to the point where I can get <code>[Observable&lt;CityMappable&gt;]</code> but I want to transform it into <code>Observable&lt;[CityMappable]&gt;</code> so I can bind it to tableview datasource.</p>
  
  <pre><code>let favCitiesID: Observable&lt;[Int]&gt; = Observable.of([0,1,2])
  
  let observableCities = favCitiesID.flatMap { cityIds -&gt; Observable&lt;[CityMappable]&gt; in
          return cityIds.map{ return self.apiManager.getCurrentWeatherData(for: $0)}
  }
  </code></pre>
  
  <p>This is APIManager function definition</p>
  
  <pre><code>func getCurrentWeatherData(for cityID: Int)-&gt;Observable&lt;CityMappable&gt;
  </code></pre>