title: Pandas Secondary Axis
body: <p>I have the following data frame</p>
  
  <pre><code>    Date        A           B
  0   2017-05-31  17453139    5.865738
  1   2017-06-30  17425164    5.272728
  2   2017-07-31  17480789    4.843094
  </code></pre>
  
  <p>When I run this:</p>
  
  <pre><code>df.plot(x='Date', y='A')
  df.B.plot(secondary_y=True)
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>&gt; appdata\local\programs\python\python36\lib\site-packages\pandas\plotting\_timeseries.py
  &gt; in format_dateaxis(subplot, freq, index)
  &gt;     335             TimeSeries_TimedeltaFormatter())
  &gt;     336     else:
  &gt; --&gt; 337         raise TypeError('index type not supported')
  &gt;     338 
  &gt;     339     pylab.draw_if_interactive()
  &gt; 
  &gt; TypeError: index type not supported
  </code></pre>
  
  <p>And my graph looks like this underneath the error (blue and red should overlap):
  <a href="https://i.stack.imgur.com/pxEvB.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/pxEvB.jpg" alt="Blue and red should overlap"></a></p>