title: How to determine the length of lists in a pandas dataframe column
body: <p>How can the length of the lists in the column be determine without iteration?</p>
  <p>I have a dataframe like this:</p>
  <pre><code>                                                    CreationDate
  2013-12-22 15:25:02                  [ubuntu, mac-osx, syslinux]
  2009-12-14 14:29:32  [ubuntu, mod-rewrite, laconica, apache-2.2]
  2013-12-22 15:42:00               [ubuntu, nat, squid, mikrotik]
  </code></pre>
  <p>I am calculating the length of lists in the <code>CreationDate</code> column and making a new <code>Length</code> column like this:</p>
  <pre><code>df['Length'] = df.CreationDate.apply(lambda x: len(x))
  </code></pre>
  <p>Which gives me this:</p>
  <pre><code>                                                    CreationDate  Length
  2013-12-22 15:25:02                  [ubuntu, mac-osx, syslinux]       3
  2009-12-14 14:29:32  [ubuntu, mod-rewrite, laconica, apache-2.2]       4
  2013-12-22 15:42:00               [ubuntu, nat, squid, mikrotik]       4
  </code></pre>
  <p>Is there a more pythonic way to do this?</p>