在pandas DataFrame中将某些值替换为NaN时，如何避免数据类型转换？

import pandas as pd
import numpy as np

# 创建一个示例DataFrame
data = {'A': [1, 2, 3, 4, 5],
        'B': ['a', 'b', 'c', 'd', 'e'],
        'C': [0.1, 0.2, 0.3, 0.4, 0.5]}
df = pd.DataFrame(data)

# 将值为1和0.3的元素替换为NaN
replace_dict = {1: np.nan, 0.3: np.nan}
df = df.replace(replace_dict)

print(df)

     A  B    C
0  NaN  a  0.1
1  2.0  b  0.2
2  3.0  c  NaN
3  4.0  d  0.4
4  5.0  e  0.5