Sample each group after pandas groupby

Question

How do I sample each group after groupby operation?

import pandas as pd

df = pd.DataFrame({'a': [1,2,3,4,5,6,7],
                   'b': [1,1,1,0,0,0,0]})

grouped = df.groupby('b')

Given the above setup, I want to sample from each group, e.g., I want 30% of each group.

Answer 1

Apply a lambda and call sample with param frac:

In [2]:
df = pd.DataFrame({'a': [1,2,3,4,5,6,7],
                   'b': [1,1,1,0,0,0,0]})
​
grouped = df.groupby('b')
grouped.apply(lambda x: x.sample(frac=0.3))

Out[2]:
     a  b
b        
0 6  7  0
1 2  3  1