title: scatter plots with string arrays in matplotlib
body: <p>this seems like it should be an easy one but I can't figure it out. I have a pandas data frame and would like to do a 3D scatter plot with 3 of the columns. The X and Y columns are not numeric, they are strings, but I don't see how this should be a problem.</p>
  
  <pre><code>X= myDataFrame.columnX.values #string
  Y= myDataFrame.columnY.values #string
  Z= myDataFrame.columnY.values #float
  
  fig = pl.figure()
  ax = fig.add_subplot(111, projection='3d')
  ax.scatter(X, Y, np.log10(Z), s=20, c='b')
  pl.show()
  </code></pre>
  
  <p>isn't there an easy way to do this? Thanks.</p>