title: Get List<int> from List<Customer> using linq
body: <p>I have list of <code>customer</code> and want its <code>id</code> in separate list <code>List&lt;int&gt;</code>.</p>
  
  <p>I tried using: </p>
  
  <pre><code>customerList.Cast&lt;int&gt;.Distinct().ToList() 
  </code></pre>
  
  <p>But it dosn't work. I also want distinct customer int list.</p>
  
  <p>How can I do that using <code>LINQ</code> syntax? What changes should I do in my query?</p>