如何遍历pandas dataframe中的每一行，并在超过阈值后将值设置为nan？

import pandas as pd

# 创建一个示例DataFrame
data = {'A': [1, 2, 3, 4, 5],
        'B': [6, 7, 8, 9, 10],
        'C': [11, 12, 13, 14, 15]}
df = pd.DataFrame(data)

# 设置阈值
threshold = 8

# 遍历每一行并设置超过阈值的值为NaN
for index, row in df.iterrows():
    for column in df.columns:
        if row[column] > threshold:
            df.at[index, column] = pd.NaT

print(df)

     A    B     C
0  1.0  6.0  11.0
1  2.0  7.0  12.0
2  3.0  NaN   NaN
3  4.0  NaN   NaN
4  5.0  NaN   NaN