python - 同时替换 pandas df 中的多个值

Question

我正在尝试同时替换 pandas df 中的值。看起来该函数连续执行此操作，因此我替换的值最终被覆盖。使用下面的 X == Left，我想替换 A-D、B-C、C-B、 D-A。如果我只执行其中一个调用，效果会很好，但当我执行所有四个调用时，它就不行了。以下是我的尝试:

import pandas as pd

df = pd.DataFrame({   
    'X' : ['Left','Left','Left','Left','Right','Right','Right','Right'],
    'Y' : ['A','B','C','D','A','B','C','D'],            
    })

尝试 1:

df[(df['X'] == 'Left') & (df['Y'] == 'A')] = df['Y'].map({'A': 'D'})
df[(df['X'] == 'Left') & (df['Y'] == 'B')] = df['Y'].map({'B': 'C'})
df[(df['X'] == 'Left') & (df['Y'] == 'C')] = df['Y'].map({'C': 'B'})
df[(df['X'] == 'Left') & (df['Y'] == 'D')] = df['Y'].map({'D': 'A'})

输出:

       X  Y
0      D  D
1      C  C
2      B  B
3      A  A
4  Right  A
5  Right  B
6  Right  C
7  Right  D

尝试 2:

df.loc[(df['X'] == 'Left') & (df['Y'] == 'A'), 'Y'] = 'D'
df.loc[(df['X'] == 'Left') & (df['Y'] == 'B'), 'Y'] = 'C'
df.loc[(df['X'] == 'Left') & (df['Y'] == 'C'), 'Y'] = 'B'
df.loc[(df['X'] == 'Left') & (df['Y'] == 'D'), 'Y'] = 'A'

输出:

       X  Y
0   Left  A
1   Left  B
2   Left  B
3   Left  A
4  Right  A
5  Right  B
6  Right  C
7  Right  D

预期输出:

       X  Y
0   Left  D
1   Left  C
2   Left  B
3   Left  A
4  Right  A
5  Right  B
6  Right  C
7  Right  D

Answer 1

做替换一次:

df.Y.update(df.loc[df['X'] == 'Left','Y'].replace({'A': 'D','B': 'C','C': 'B','D': 'A'}))
df
       X  Y
0   Left  D
1   Left  C
2   Left  B
3   Left  A
4  Right  A
5  Right  B
6  Right  C
7  Right  D