相关疑难解决方法(0)

我正在尝试用NaN值替换数据中的一些空列表.但是如何在表达式中表示一个空列表？

import numpy as np
import pandas as pd
d = pd.DataFrame({'x' : [[1,2,3], [1,2], ["text"], []], 'y' : [1,2,3,4]})
d

    x           y
0   [1, 2, 3]   1
1   [1, 2]      2
2   [text]      3
3   []          4



d.loc[d['x'] == [],['x']] = d.loc[d['x'] == [],'x'].apply(lambda x: np.nan)
d

ValueError: Arrays were different lengths: 4 vs 0

而且,我想选择[text]使用d[d['x'] == ["text"]]带有ValueError: Arrays were different lengths: 4 vs 1错误,但选择3使用d[d['y'] == 3]是正确的.为什么？