为什么 pandas df.loc + lambda不起作用? [英] Why does not work pandas df.loc + lambda?

问题描述

我已经从csv文件创建了熊猫框架. 我想选择使用lambda的行. 但这是行不通的. 我使用了此熊猫手册. 例外:

I have created pandas frame from csv file. And I want to select rows use lambda. But it does not work. I use this pandas manual. exception:

出什么问题了? 谢谢.

what is problem? thanks.

推荐答案

正如@BrenBam在评论中说的那样，此语法已在0.18.1中添加，并且在以前的版本中不起作用.

As @BrenBam has said in the comment this syntax was added in 0.18.1 and it won't work in previous versions.

可调用选择:

.loc，.iloc，.ix和[]索引也可以接受可调用的 索引器.可调用对象必须是带有一个参数的函数( 调用Series，DataFrame或Panel)，并为 索引.

.loc, .iloc, .ix and also [] indexing can accept a callable as indexer. The callable must be a function with one argument (the calling Series, DataFrame or Panel) and that returns valid output for indexing.

示例(0.18.1版):

Example (version 0.18.1):

In [10]: df
Out[10]:
   a  b  c
0  1  4  2
1  2  2  4
2  3  4  0
3  0  2  3
4  3  0  4

In [11]: df.loc[lambda df: df.a == 3]
Out[11]:
   a  b  c
2  3  4  0
4  3  0  4

对于< = 0.18.0版本，您不能使用Selection by callable:

For versions <= 0.18.0 you can't use Selection by callable:

请改用这种方式:

df.loc[df['Date'] == '2003-01-01 00:00:00', ['Date']]

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