如何创建一个混合了两个变量的自定义聚合函数的Pandas交叉表？

import pandas as pd
import numpy as np

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)

def custom_agg(x):
    return np.sum(x) / np.mean(x)

cross_tab = pd.crosstab(df['A'], df['B'], values=df['C'], aggfunc=custom_agg)

print(cross_tab)