title: Collection to string using linq
body: <p>I have a class</p>
  
  <pre><code>public class Person
  {
      public string FirstName { get; set; }
      public string LastName { get; set; }   
  }
  
  List&lt;Person&gt; PersonList = new List&lt;Perso&gt;();
  PersonList.Add(new Person() { FirstName = "aa", LastName = "AA" } );
  PersonList.Add(new Person() { FirstName = "bb", LastName = "BB" } );
  </code></pre>
  
  <p>I'd like get a string with a comma separator for the LastName, using Linq, the result look like:
  AA,BB </p>
  
  <p>Thanks,</p>