python - Stratified Sampling in Pandas

Question

I've looked at the Sklearn stratified sampling docs as well as the pandas docs and also Stratified samples from Pandas and sklearn stratified sampling based on a column but they do not address this issue.

Im looking for a fast pandas/sklearn/numpy way to generate stratified samples of size n from a dataset. However, for rows with less than the specified sampling number, it should take all of the entries.

Concrete example:

Thank you! :)

question from:https://stackoverflow.com/questions/44114463/stratified-sampling-in-pandas

Answer 1

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