title: Union two list by property
body: <p>I would like to merge two list without duplicates. It should distinct only by one property.</p>
  
  <p>I have a class:</p>
  
  <pre><code>public class Test
  {
      public int Id { get; set; }
      public string Prop { get; set; }
      public string Type { get; set; }
  }
  </code></pre>
  
  <p>I have two lists which I would like to merge without duplicates by Type. So, firstly I want to take everything from list 1 and then from list 2 when Type doesn't exist in list 1.</p>
  
  <p>I've tried union.</p>