pandas中的groupby打乱了行索引

import pandas as pd

# 创建一个示例DataFrame
data = {'A': ['foo', 'bar', 'foo', 'bar', 'foo', 'bar', 'foo', 'foo'],
        'B': ['one', 'one', 'two', 'two', 'two', 'one', 'two', 'one'],
        'C': [1, 2, 3, 4, 5, 6, 7, 8],
        'D': [10, 20, 30, 40, 50, 60, 70, 80]}
df = pd.DataFrame(data)

# 使用groupby对列'A'进行分组，并对列'C'求和
grouped = df.groupby('A', as_index=False)['C'].sum()

print(grouped)

     A   C
0  bar  12
1  foo  16