See gist as a notebook here: http://nbviewer.ipython.org/gist/ghl3/8760132/notebook.ipynb
Create a simple DataFrame:
df = pandas.DataFrame({'user_id':[1, 1, 2, 2, 3, 3],
'type':['A','A','A','A','B','B'],
'val':[100, 200, 150, 30, 300, 75]})
df.head()