如何将两列（具有相同值的第一列）插入数据框

Question

下面是解释我想要的简单示例。我需要将列从第一个数据帧添加到其他：

import pandas as pd
df = pd.DataFrame({'Animal': ['Falcon', 'Falcon',
                               'Parrot', 'Parrot'],
                    'Max Speed': [380., 370., 24., 26.]})

outlets = pd.DataFrame(columns = ['mac', 'x'])

outlets = outlets.append({'mac' : 1, 'x' : [*df.Animal]}, ignore_index=True)
outlets

输出为：

   mac       x
0   1   [Falcon, Falcon, Parrot, Parrot]

但是我真正想要的是：

   mac       x
0   1      Falcon
1   1      Falcon
2   1      Parrot
3   1      Parrot

请告诉我我该怎么做...

Answer 1

输出：

        x  mac
0  Falcon    1
1  Falcon    1
2  Parrot    1
3  Parrot    1

Answer 2

效率低：

import pandas as pd
df = pd.DataFrame({'Animal': ['Falcon', 'Falcon',
                               'Parrot', 'Parrot'],
                    'Max Speed': [380., 370., 24., 26.]})

outlets = pd.DataFrame(columns = ['mac', 'x'])

for animal in [*df.Animal]:
    outlets = outlets.append({'mac': 1,'x': animal}, ignore_index=True)
print(outlets)

更有效：

import pandas as pd
df = pd.DataFrame({'Animal': ['Falcon', 'Falcon',
                               'Parrot', 'Parrot'],
                    'Max Speed': [380., 370., 24., 26.]})


outlets = pd.concat(
    [pd.DataFrame([[1, animal]], columns=['mac', 'x']) for animal in [*df.Animal]],
    ignore_index=True)
print(outlets)

输出：

Less efficient:
   mac       x
0    1  Falcon
1    1  Falcon
2    1  Parrot
3    1  Parrot

More efficient:
  mac       x
0   1  Falcon
1   1  Falcon
2   1  Parrot
3   1  Parrot