title: How can I choose which subscribed observers to be emitted?
body: <p>I have a service to communicate with server using SignalR. Service consumers subscribe to a Rxjs's Subject but I what I want is they should pass some additional data( a string in this case) and after service received data from server could choose which subscriber to be executed by calling next() method. </p>
  
  <p>I tried to write a new subscribe method and store every subscription but there is no way to link subscriptions and observer. Here is my code :</p>
  
  <pre><code>private subscriptions = new Array&lt;{registerationName:string,subscription:Subscription}&gt;();
  private receiver = new Subject(); 
  
  public subscribe(registerationName:string ,next?: (value: {}) =&gt; void, error?: (error: any) =&gt; void): Subscription
  {
       var s = this.receiver.subscribe(next,error);
       this.subscriptions.push({registerationName:registerationName,subscription:s});
       return s;
  }
  </code></pre>
  
  <p>Obviously above approach does not work. What exactly I want to do is something like this :</p>
  
  <pre><code>this.receiver.observer.where(p=&gt;p.registerationName==stringFromServer).next({...}) 
  </code></pre>