在groupby之后的1列内将2个值相减

import pandas as pd

# 创建一个示例数据集
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函数按照列A进行分组，并使用transform函数对列C进行操作
df['C_diff'] = df.groupby('A')['C'].transform(lambda x: x.diff())

# 打印结果
print(df)

     A    B  C   D  C_diff
0  foo  one  1  10     NaN
1  bar  one  2  20     NaN
2  foo  two  3  30     2.0
3  bar  two  4  40     2.0
4  foo  two  5  50     2.0
5  bar  one  6  60     2.0
6  foo  two  7  70     2.0
7  foo  one  8  80     2.0