如何在pandas数据框中为不同的组分配唯一ID？

import pandas as pd

data = {'Group': ['A', 'A', 'B', 'B', 'B', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

df['ID'] = df.groupby('Group').cumcount() + 1

import pandas as pd

data = {'Group': ['A', 'A', 'B', 'B', 'B', 'C'],
        'Value': [1, 2, 3, 4, 5, 6]}
df = pd.DataFrame(data)

df['ID'] = df.groupby('Group').cumcount() + 1

print(df)

  Group  Value  ID
0     A      1   1
1     A      2   2
2     B      3   1
3     B      4   2
4     B      5   3
5     C      6   1