Pandas Chaining - Second most common value

pandas_nth.md

link

import pandas as pd

df = pd.DataFrame({'x': [1, 1, 1, 2, 2, 3],
                   'y': [1, 2, 3, 1, 2, 1],
                   'n': [3, 2, 1, 1, 2, 1]})

df

	x	y	n
0	1	1	3
1	1	2	2
2	1	3	1
3	2	1	1
4	2	2	2
5	3	1	1

# wrap the function into pipe
# a handy way to chain functions 
# pipe can return arbitrary objects
# and can be handy in some awkward pandas operations

df.groupby('x').y.pipe(lambda df: pd.DataFrame({'frequency' : df.sum(), 
                                                'second' : df.nth(1)}
                                              )
                      )

	frequency	second
x
1	6	2.0
2	3	2.0
3	1	NaN