title: How to merge a list of lists with same type of items to a single list of items?
body: <p>The question is confusing, but it is much more clear as described in the following codes:</p>
  
  <pre><code>   List&lt;List&lt;T&gt;&gt; listOfList;
     // add three lists of List&lt;T&gt; to listOfList, for example
     /* listOfList = new {
          { 1, 2, 3}, // list 1 of 1, 3, and 3
          { 4, 5, 6}, // list 2
          { 7, 8, 9}  // list 3
          };
     */
     List&lt;T&gt; list = null;
     // how to merger all the items in listOfList to list?
     // { 1, 2, 3, 4, 5, 6, 7, 8, 9 } // one list
     // list = ???
  </code></pre>
  
  <p>Not sure if it possible by using C# LINQ or Lambda? </p>
  
  <p><strong>Essentially, how can I concatenate or "<em>flatten</em>" a list of lists?</strong></p>