如何在Pandas中有条件地查找NaN

import pandas as pd
import numpy as np

# 创建一个包含NaN值的DataFrame
data = {'A': [1, 2, np.nan, 4],
        'B': [np.nan, 2, 3, np.nan],
        'C': [1, 2, 3, 4]}
df = pd.DataFrame(data)

# 使用isnull()函数查找NaN值
nan_df = df.isnull()
print(nan_df)

# 使用notnull()函数查找非NaN值
not_nan_df = df.notnull()
print(not_nan_df)

# 有条件地查找NaN值
condition = df['A'].isnull()
nan_values = df[condition]
print(nan_values)

       A      B      C
0  False   True  False
1  False  False  False
2   True  False  False
3  False   True  False

       A      B     C
0   True  False  True
1   True   True  True
2  False   True  True
3   True  False  True

    A   B  C
2 NaN NaN  3