在pandas groupby之后对每组进行采样

问题描述

我知道这一定在某些地方得到了回答，但我就是找不到.

I know this must have been answered some where but I just could not find it.

问题:groupby操作后对每组进行采样.

Problem: 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')

# now sample from each group, e.g., I want 30% of each group

推荐答案

应用 lambda 并调用 sample 带有参数 frac:

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

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