title: LINQ. Update one dictionary from corresponding values in another joined by key
body: <p>I have to dictionaries </p>
  
  <pre><code>dic1&lt;double, double&gt;
  dic2&lt;double, double&gt;
  </code></pre>
  
  <p>The length might not match. So I need to update values in dic1 from dic2 joined by dic1.key == dic2.key... But preserve those values in dic1 which has no corresponding key in dic2.</p>
  
  <p>.NET is 3.5</p>