title: Find All Rows in DataTable Where Column Value is NOT Unique Using Linq Query
body: <p>I am attempting to write a Linq to SQL query that returns all rows in a DataTable where a columns value (TxnNumber) is not unique.  So far, I have the Linq to SQL below where dt is the DataTable that contains the field TxnNumber.  I think that I am pretty close but, intellisense is complaining about the CONTAINS clause.  I have tried specifying that I only want to return the TxnNumber field in the sub-select but, it will not compile.  Can anyone see what I am doing wrong?</p>
  
  <pre><code>dt.AsEnumerable().Where(u =&gt; u.TxnNumber.Contains (dt.AsEnumerable().GroupBy(t =&gt; t.TxnNumber).Count() &gt; 1));
  </code></pre>