groupby().nth() missing docs, throws errors when multiple columns in group

[nickeubank]

Hi All!

I've been using .nth(), and found a couple issues (though it's extremely useful in general!). In particular, I couldn't find any help documentation (in python) for the function.

Also, I ran into issues with I had a two-column groupby. for example:

df = pd.DataFrame([[1,2,3],[1,5,6], [7,8,6]], columns = ['col1','col2','col3'])
df.groupby('col1').nth([0,1]) 

Is ok

In [23]: df.groupby(['col1', 'col2'], as_index = False).nth([0,1])
Out[23]: 
   col1  col2  col3
0     1     2     3
1     1     5     6
2     7     8     6

In [24]: df.groupby(['col1', 'col2']).nth([0,1])
ValueError: Length of new names must be 1, got 2

[jreback]

docs are here: http://pandas.pydata.org/pandas-docs/stable/groupby.html#taking-the-nth-row-of-each-group

[jreback]

@nickeubank that is a newish feature and looks a bit buggy. Master shows slightly differently so I changed the report a bit.

PR's are welcome

[nickeubank]

PR = problem reports?

Thanks on docs -- that's where I found function. I was thinking of in python (i.e. what you get when you hit df.groupby('a').nth? in iPython.

[jreback]

closed by #9090