循环遍历分层索引时.loc()的赋值

import pandas as pd

# 创建一个带有分层索引的DataFrame
data = {'A': [1, 2, 3, 4],
        'B': [5, 6, 7, 8],
        'C': [9, 10, 11, 12]}
index = pd.MultiIndex.from_tuples([('Group1', 'A'), ('Group1', 'B'), ('Group2', 'A'), ('Group2', 'B')])
df = pd.DataFrame(data, index=index)

# 循环遍历分层索引并使用.loc()进行赋值
for group, label in df.index:
    df.loc[(group, label), 'C'] = df.loc[(group, label), 'A'] + df.loc[(group, label), 'B']

print(df)

           A  B   C
Group1 A   1  5   6
       B   2  6   8
Group2 A   3  7  10
       B   4  8  12