title: Sort Pandas dataframe by list size not A-Z
body: <p>I have a dataframe that looks like this:</p>
  
  <pre><code>username          group
  user1             [A]
  user2             [B, C]
  user3             [A, B, C]
  user4             [A, B]
  </code></pre>
  
  <p>I want the result to look like this:</p>
  
  <pre><code>username          group
  user3             [A, B, C]
  user4             [A, B]
  user2             [B, C]
  user1             [A]
  </code></pre>
  
  <p>I've looked up the documentation for sort_values and it seems to cover mainly 0-9 or A-Z sorting.. thanks in advance</p>