title: Remove duplicates from list based on multiple fields or columns
body: <p>I have a list of type MyClass</p>
  
  <pre><code>public class MyClass
  {
     public string prop1 {} 
     public int prop2 {} 
     public string prop3 {} 
     public int prop4 {} 
     public string prop5 {} 
     public string prop6 {} 
     ....
  }
  </code></pre>
  
  <p>This list will have duplicates. I want to find and remove items from this list where prop1, prop2 and prop3 are duplicates. It doesnt matter if the other properties are duplicates</p>
  
  <p>This is what I have tried that is not working.</p>
  
  <pre><code>List&lt;MyClass&gt; noDups = myClassList.GroupBy(d =&gt; new {d.prop1,d.prop2,d.prop3} ).Where(g =&gt; g.Count() &gt; 1).Select(g=&gt; g.Key);
  </code></pre>
  
  <p>I dont want to use any third party tools for this. Only pure linq.</p>