title: RxJava + Retrofit : distinguish each request in multiple request call API
body: <p>I have a list of city and I'd like to find the weather in each city.
  e.g my list is cities = {london, berlin, headington}
  so, my code is call api service for each city.</p>
  
  <p>in my activity, this is how I request the weather each city :</p>
  
  <pre><code>for(String element : cities) {
      presenter.getApi(element);
  }
  </code></pre>
  
  <p>and in the presenter, which is implement the observer, this is the code to respond the result :</p>
  
  <pre><code>@Override
  public void onNext (ResultObject result) {
      // getName() function return city name
      log.d("Result", result.getMain().getName() + result.getWeather().getDescription();
  }
  </code></pre>
  
  <p>because this function (onNext) <strong>not</strong> come respectively as the request (we request london first then berlin then headington), so I don't know how to distinguish my london weather request with the berlin.</p>
  
  <p>Also, in the API respond, its not always attached the request city. If I request Headington, the respond is Oxford.</p>
  
  <p>Api service using Get, the link below (return an observable)
  <a href="http://api.openweathermap.org/data/2.5/weather?q=headington&amp;appid=90faa1669716319e787ca1ab5da48cbc" rel="nofollow noreferrer">http://api.openweathermap.org/data/2.5/weather?q=headington&amp;appid=90faa1669716319e787ca1ab5da48cbc</a></p>