title: Creating contour plot from Pandas multi-index dataframe
body: <p>How do I create a contour plot from the following Pandas dataframe named think_or_feel:</p>
  <pre><code>              think     feel
  cNEU    cOPN        
  y         n     27      20
  n         n     40      23
  y         y     43      25
  n         y     97      63
  </code></pre>
  <p>I have tried the following:</p>
  <pre><code>X=think_or_feel.columns
  Y=think_or_feel.index 
  Z=think_or_feel.values
  x,y=np.meshgrid(X, Y)
  plt.contourf(x,y,Z)
  </code></pre>
  <p>I get the following error:
  <code>unhashable type: 'numpy.ndarray'</code></p>
  <p>I'd really appreciate any help on this.</p>