Pandas将FutureWarning切成0.21.0

Question

我正在尝试选择数据帧子集的子集,仅选择一些列,并对行进行过滤.

df.loc[df.a.isin(['Apple', 'Pear', 'Mango']), ['a', 'b', 'f', 'g']]

但是,我收到错误:

Passing list-likes to .loc or [] with any missing label will raise
KeyError in the future, you can use .reindex() as an alternative.

现在切片和过滤的正确方法是什么？

Answer 1

这是一个引入的变化v0.21.1,并在文档中详细解释-

以前,使用标签列表进行选择,其中缺少一个或多个标签将始终成功,返回NaN缺少的标签.这将显示一个FutureWarning.在未来,这将提高 KeyError(GH15747).此警告将触发a DataFrame或a Series用于.loc[]或[[]]在传递标签列表时至少丢失1个标签.

例如,

df

     A    B  C
0  7.0  NaN  8
1  3.0  3.0  5
2  8.0  1.0  7
3  NaN  0.0  3
4  8.0  2.0  7

在你做的时候尝试某种切片 -

df.loc[df.A.gt(6), ['A', 'C']]

     A  C
0  7.0  8
2  8.0  7
4  8.0  7

没问题.现在,尝试替换C不存在的列标签 -

df.loc[df.A.gt(6), ['A', 'D']]
FutureWarning: Passing list-likes to .loc or [] with any missing label will raise
KeyError in the future, you can use .reindex() as an alternative.

     A   D
0  7.0 NaN
2  8.0 NaN
4  8.0 NaN

因此,在您的情况下,错误是由于您传递给的列标签loc.再看看他们.