user1700890 user1700890 - 1 year ago 123
Python Question

How to group by one column and sort the values of another column?

Here is my dataframe

import pandas as pd
df = pd.DataFrame({'A': ['one', 'one', 'two', 'two', 'one'] ,
'B': ['Ar', 'Br', 'Cr', 'Ar','Ar'] ,
'C': ['12/15/2011', '11/11/2001', '08/30/2015', '07/3/1999','03/03/2000' ],

My goal is to group by column
and sort within grouped results by column

Here is what I came up with:

sort_group = df.sort_values('B').groupby('A')

I was hoping that grouping operation would not distort order, but it does not work and also returns not a dataframe, but

<pandas.core.groupby.DataFrameGroupBy object at 0x0000000008B190B8>

Any suggestions?

Answer Source
df.groupby('A').apply(lambda x: x.sort_values('B'))

gives you the desired output:

         A   B           C  D
one 0  one  Ar  12/15/2011  1
    4  one  Ar  03/03/2000  5
    1  one  Br  11/11/2001  7
two 3  two  Ar   07/3/1999  4
    2  two  Cr  08/30/2015  3

You can apply sort_values not directly to a groupby object but you need an apply.

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