如何在pandas中用字符串值替换NaN

import pandas as pd

# 创建一个包含NaN值的DataFrame
data = {'A': [1, 2, None, 4, 5],
        'B': [None, 'a', 'b', None, 'c']}
df = pd.DataFrame(data)

# 用字符串值替换NaN
df_filled = df.fillna('missing')

print(df_filled)

        A        B
0       1  missing
1       2        a
2  missing        b
3       4  missing
4       5        c