title: Filter WhereSelectEnumerableIterator of Generic List using Linq
body: <p>I have the following code which builds a Generic List of Abc from a database query.</p>
  
  <pre><code>List&lt;Abc&gt; lAbc = DB.GetAbc();
  
  var lRawData = from r in lAbc
                 group r by r.Stage1Check into s
                 select s.ToList();
  </code></pre>
  
  <p>This gives me a WhereSelectEnumerableIterator of Generic List of Abc - which is ok.  I then write this data to an Excel sheet.</p>
  
  <p>The problem is that I need to further filter this data.  The object Abc contains a property called FilterProp which is a boolean.  What I can't figure out is how to use Linq to filter lRawData where the FilterProp is true?</p>
  
  <p>Mark</p>