title: How can I use ":" in LINQ group by conditions
body: <p>I have 2 variable use like condition to group by in a data list
      string FileNo = "";
      string FileName = "";  </p>
  
  <p>Because FileNo and FileName may be blank
  So when I have a data list looks like below:
      List DataList = new List();</p>
  
  <p>I want to make sure FileNo and FileName not blank then I will use them in group by</p>
  
  <p>I don't know how to embed them in LINQ syntax. Some etc looks like this:</p>
  
  <pre><code>var TotalDuplicate = GridList.GroupBy(x,y =&gt; "".Equals(FileNo) : x.FileNo, 
                                               "".Equals(FileName) : y.FileName
                          .Count(x =&gt; x.Count() &gt; 1);
  </code></pre>