title: pandas plot dataframe as multiple bar charts
body: <p>This is my pandas dataframe <code>df</code>: </p>
  
  <pre><code>          ab             channel   booked
  0    control             book_it     466
  1    control          contact_me     536
  2    control             instant     17
  3  treatment             book_it     494
  4  treatment          contact_me     56
  5  treatment             instant     22
  </code></pre>
  
  <p>I want to plot 3 groups of bar chart (according to <code>channel</code>):</p>
  
  <p>for each channel:
  plot control booked value vs treatment booked value. </p>
  
  <p>hence i should get 6 bar charts, in 3 groups where each group has control and treatment booked values. </p>
  
  <p>SO far i was only able to plot booked but not grouped by ab:</p>
  
  <pre><code>ax = df_conv['booked'].plot(kind='bar',figsize=(15,10), fontsize=12)
  ax.set_xlabel('dim_contact_channel',fontsize=12)
  ax.set_ylabel('channel',fontsize=12)
  plt.show()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/5Im7P.png" rel="noreferrer"><img src="https://i.stack.imgur.com/5Im7P.png" alt="enter image description here"></a></p>
  
  <p>This is what i want (only show 4 but this is the gist):
  <a href="https://i.stack.imgur.com/VAOS9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/VAOS9.png" alt="enter image description here"></a></p>