使用查询将 np.nans 分配给 Pandas 列的行

Question

当满足某些条件时，我想将 NaN 分配给 Pandas 数据框中的列的行。

以下是一些可重现的示例：

'{"Price":{"1581292800000":21.6800003052,"1581379200000":21.6000003815,"1581465600000":21.6000003815,"1581552000000":21.6000003815,"1581638400000":22.1599998474,"1581984000000":21.9300003052,"1582070400000":22.0,"1582156800000":21.9300003052,"1582243200000":22.0200004578,"1582502400000":21.8899993896,"1582588800000":21.9699993134,"1582675200000":21.9599990845,"1582761600000":21.8500003815,"1582848000000":22.0300006866,"1583107200000":21.8600006104,"1583193600000":21.8199996948,"1583280000000":21.9699993134,"1583366400000":22.0100002289,"1583452800000":21.7399997711,"1583712000000":21.5100002289},"Target10":{"1581292800000":22.9500007629,"1581379200000":23.1000003815,"1581465600000":23.0300006866,"1581552000000":22.7999992371,"1581638400000":22.9599990845,"1581984000000":22.5799999237,"1582070400000":22.3799991608,"1582156800000":22.25,"1582243200000":22.4699993134,"1582502400000":22.2900009155,"1582588800000":22.3248996735,"1582675200000":null,"1582761600000":null,"1582848000000":null,"1583107200000":null,"1583193600000":null,"1583280000000":null,"1583366400000":null,"1583452800000":null,"1583712000000":null}}'

在这个特定的玩具示例中，当“Target10”列具有 NaN 时，我想将 NaN 分配给“价格”列。 （一般情况下情况可能更复杂）

这行代码实现了特定目标：

toy_data.Price.where(toy_data.Target10.notnull(), toy_data.Target10)

但是，当我尝试使用查询并将 NaN 分配给目标列时，我失败了：

toy_data.query('Target10.isnull()', engine = 'python').Price = np.nan

上面的行使toy_data保持不变。

为什么会这样以及我应该如何使用 query 替换特定行中的值？

Answer 1

一种方法是 -

import numpy as np 
toy_data['Price'] = np.where(toy_data['Target10'].isna(), np.nan, toy_data['Price'])