title: Pushing new observables based on input from previous in RxJS
body: <p>I'm finding it difficult to compose an subject or observable where I have validation. This is the nature of Functional programming, but it seems that Reactive Programming only takes care of each piece of data. Also, the examples are a bit too generalistic, no real world example that covers a lot of aspects, though this is a personal opinion. </p>
  
  <p>I'd like to send another value to the observer based on the previous one, but I can't find out how to achieve this. </p>
  
  <pre><code> Rx.Observable.create( function(obs) {
    obs.next(1)
    // if value is one, compile 3, if not, respond with 2
    obs.next(someVal)
    obs.onCompleted()
  });
  </code></pre>