从pandas DataFrame MultiIndex中选择命名索引级别

import pandas as pd

# 创建一个带有MultiIndex的DataFrame
data = {'A': [1, 2, 3, 4],
        'B': [5, 6, 7, 8],
        'C': [9, 10, 11, 12]}
index = pd.MultiIndex.from_tuples([('foo', 'one'), ('foo', 'two'), ('bar', 'one'), ('bar', 'two')],
                                  names=['first', 'second'])
df = pd.DataFrame(data, index=index)

# 获取第一级索引的值
first_level_values = df.index.get_level_values('first')
print(first_level_values)

# 获取第二级索引的值
second_level_values = df.index.get_level_values('second')
print(second_level_values)

Index(['foo', 'foo', 'bar', 'bar'], dtype='object', name='first')
Index(['one', 'two', 'one', 'two'], dtype='object', name='second')