title: GroupBy with linq method syntax (not query syntax)
body: <p>How would the following query look if I was using the extension method syntax?</p>
  
  <pre><code>var query = from c in checks
  group c by string.Format("{0} - {1}", c.CustomerId, c.CustomerName) 
  into customerGroups
  select new { Customer = customerGroups.Key, Payments = customerGroups }
  </code></pre>