使用字符值在熊猫中创建新行

In [200]: df
Out[200]:
     col1         col2
0  animal  cat;dog;cat
1  animal          dog
2  animal         fish
3   color  black;green
4   color          red

In [201]: (df.set_index('col1')
             .col2.str.split(';', expand=True)
             .stack()
             .reset_index(level=1, drop=True)
             .reset_index(name='col2'))
Out[201]:
     col1   col2
0  animal    cat
1  animal    dog
2  animal    cat
3  animal    dog
4  animal   fish
5   color  black
6   color  green
7   color    red

使用 numpy.repeat 和 itertools.chain :

import numpy as np
from itertools import chain

split = df['col2'].str.split(';')

res = pd.DataFrame({'col1': np.repeat(df['col1'], split.map(len)),
                    'col2': list(chain.from_iterable(split))})

print(res)

     col1   col2
0  animal    cat
0  animal    dog
0  animal    cat
1  animal    dog
2  animal   fish
3   color  black
3   color  green
4   color    red