你可以试试这个：

import numpy as np

new_df = pd.DataFrame(np.repeat(df.values, len(lst), axis=0), columns=df.columns)
new_lst = lst * len(df)
new_df['group'] = new_lst
print(new_df)

输出：

sample           values  group
0  sample 1  [0.2, 0.3, 0.5]      0
1  sample 1  [0.2, 0.3, 0.5]      1
2  sample 1  [0.2, 0.3, 0.5]      2
3  sample 2  [0.3, 0.3, 0.4]      0
4  sample 2  [0.3, 0.3, 0.4]      1
5  sample 2  [0.3, 0.3, 0.4]      2

使用十字merge：

out = df.drop(columns='group').merge(pd.Series(lst, name='group'), how='cross')

输出：

sample           values  group
0  sample 1  [0.2, 0.3, 0.5]      0
1  sample 1  [0.2, 0.3, 0.5]      1
2  sample 1  [0.2, 0.3, 0.5]      2
3  sample 2  [0.3, 0.3, 0.4]      0
4  sample 2  [0.3, 0.3, 0.4]      1
5  sample 2  [0.3, 0.3, 0.4]      2