title: Plotting: qcut then groupby two variables
body: <p>I have the following dataset:</p>
  <pre><code>df = pd.DataFrame({'cls': [1,2,2,1,2,1,2,1,2,1,2],
                     'x': [10,11,21,21,8,1,4,3,5,6,2],
                     'y': [10,1,2,2,5,2,4,3,8,6,5]})
  
  df['bin'] = pd.qcut(np.array(df['x']), 4)
  a = df.groupby(['bin', 'cls'])['y'].mean()
  a
  </code></pre>
  <p>This gives me</p>
  <pre><code>bin           cls
  (0.999, 3.5]  1       2.5
                2       5.0
  (3.5, 6.0]    1       6.0
                2       6.0
  (6.0, 10.5]   1      10.0
                2       5.0
  (10.5, 21.0]  1       2.0
                2       1.5
  Name: y, dtype: float64
  </code></pre>
  <p>I want to plot the right-most column (that is, the average of <code>y</code> per <code>cls</code> per bin) per bin per class. That is, for each bin we have two values of <code>y</code> that I would like to plot as points/scatters. Is that possible using matplotlib or seaborn?</p>