Multi-key groupby fails with multiple functions
Chris Jordan-Squire said:

If I had some DataFrame with a bunch of columns, including, say
'char1', 'char2', and 'float' then

df.groupby('char1')['float'].agg([np.mean, np.std])

works but

df.groupby(['char1', 'char2'])['float'].agg([np.mean, np.std])

throws TypeError: 'list' object is not callable.
