Stratified Sampling in Pandas

by

Use min when passing the number to sample. Consider the dataframe df

df = pd.DataFrame(dict(
        A=[1, 1, 1, 2, 2, 2, 2, 3, 4, 4],
        B=range(10)
    ))

df.groupby('A', group_keys=False).apply(lambda x: x.sample(min(len(x), 2)))

   A  B
1  1  1
2  1  2
3  2  3
6  2  6
7  3  7
9  4  9
8  4  8

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