title: LINQ GroupBy return List as result
body: <p>I have a List containing Transaction objects. What I am trying to do is find the transactions in said List that have the same transaction.Buyer.UserID and group them together into a List of Lists. </p>
  
  <p>Each Sub-List item will contain multiple transaction objects where the transaction.Buyer.UserID is the same.</p>
  
  <p>What I have so far is:</p>
  
  <pre><code>            var _ordersToCombine = 
              _transactions.GroupBy(transaction =&gt; transaction.Buyer.UserID).Select(transaction =&gt; transaction);
  </code></pre>
  
  <p>What I have coming in:</p>
  
  <pre><code>List&lt;Transaction&gt;:
      Transaction { Buyer.UserID = "User1" ...}
      Transaction { Buyer.UserID = "User2" ...}
      Transaction { Buyer.UserID = "User1" ...}
      Transaction { Buyer.UserID = "User3" ...}
      Transaction { Buyer.UserID = "User4" ...}
      Transaction { Buyer.UserID = "User3" ...}
  </code></pre>
  
  <p>What I expect it to return is:</p>
  
  <pre><code>List&lt;List&lt;Transaction&gt;&gt;:
      List&lt;Transaction&gt;:
          Transaction { Buyer.UserID = "User1" ...}
          Transaction { Buyer.UserID = "User1" ...}
      List&lt;Transaction&gt;:
          Transaction { Buyer.UserID = "User3" ...}
          Transaction { Buyer.UserID = "User3" ...}
  </code></pre>
  
  <p>...And also delete these Transactions from the main list, so in this example the main list would then look like:</p>
  
  <pre><code>List&lt;Transaction&gt;:
      Transaction { Buyer.UserID = "User2" ...}
      Transaction { Buyer.UserID = "User4" ...}
  </code></pre>
  
  <p>Linq is a new concept for me that I am trying to get my head around.</p>