title: How to get duplicate items from a list using LINQ?
body: <p>I'm having a <code>List&lt;string&gt;</code> like:</p>
  
  <pre><code>List&lt;String&gt; list = new List&lt;String&gt;{"6","1","2","4","6","5","1"};
  </code></pre>
  
  <p>I need to get the duplicate items in the list into a new list. Now I'm using a nested <code>for</code> loop to do this.</p>
  
  <p>The resulting <code>list</code> will contain <code>{"6","1"}</code>.</p>
  
  <p>Is there any idea to do this using <a href="http://en.wikipedia.org/wiki/Language_Integrated_Query" rel="noreferrer">LINQ</a> or <a href="https://en.wikipedia.org/wiki/Anonymous_function" rel="noreferrer">lambda expressions</a>?</p>