title: Sort lists in a Pandas Dataframe column
body: <p>I have a Dataframe column which is a collection of lists</p>
  
  <pre><code>    a
  ['a', 'b']
  ['b', 'a']
  ['a', 'c']
  ['c', 'a']
  </code></pre>
  
  <p>I would like to use this list to group by its unique values (['a', 'b'] &amp; ['a', 'c']). However, this generates an error </p>
  
  <pre><code>TypeError: unhashable type: 'list'
  </code></pre>
  
  <p>Is there any way around this. Ideally I would like to sort the values in place and create an additional column of a concatenated string.</p>