title: Combine Observable with second Observable which uses results from from the first one
body: <p>I have two methods returning Observable:</p>
  
  <pre><code>Observable&lt;String&gt; firstObservable();
  Observable&lt;String&gt; secondObservable(String value);
  </code></pre>
  
  <p>For each result from the first Observable I get new instance of the second Observable. For each result from the second observable I would return object with combined results.</p>
  
  <pre><code>firstObservable -&gt;  x----x----x----x----x
                       \    \    \    \    \
  secondObservable -&gt;   y(x)-y(x)-y(x)-y(x)-y(x)
                        \     \     \     \     \
  result -&gt;             {x,y}-{x,y}-{x,y}-{x,y}-{x,y}
  </code></pre>
  
  <p>How can this be done?</p>