title: What is the implementing class for IGrouping?
body: <p>I am trying create a WCF Data Services ServiceOperation that does grouping on the server side and then sends the data down to the client.</p>
  
  <p>When I try to call it (or even connect to the service) I get an error.  It says that it can't construct an interface.</p>
  
  <p>The only interface I am using is IGrouping.  </p>
  
  <p>What is a/the actual class for this interface?</p>
  
  <hr>
  
  <p><strong>Update:</strong></p>
  
  <p>I checked the type while debugging a sample app and it told me it was:</p>
  
  <pre><code>System.Linq.Lookup&lt;TKey,TElement&gt;.Grouping
  </code></pre>
  
  <p>But what assembly is it in? </p>