title: Iterate on Groupby Object's fields
body: <p>I want to be able to iterate on a groupby object:</p>
  
  <pre><code>    grouped = df.groupby('zzz')
      question_list = [a, 
                       b,
                       c]
  </code></pre>
  
  <p>How can I get a list of the values for the following:</p>
  
  <pre><code>    grouped.a
      grouped.b
      grouped.c
  </code></pre>
  
  <p>but using a for-loop? </p>