python - Pandas 使用 0.21.0 对 FutureWarning 进行切片

Question

我正在尝试选择数据框子集的子集，仅选择一些列，然后对行进行过滤。

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

但是，我收到了错误:

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

TL;DR:列标题名称中可能存在拼写错误或拼写错误。

这是 v0.21.1 中引入的更改，已在 docs 中进行了说明。长篇大论-

Previously, selecting with a list of labels, where one or more labels were missing would always succeed, returning NaN for missing labels. This will now show a FutureWarning. In the future this will raise a KeyError (GH15747). This warning will trigger on a DataFrame or a Series for using .loc[] or [[]] when passing a list-of-labels with at least 1 missing label.

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

在你做的时候尝试一些切片 -

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，尝试用不存在的列标签替换 C -

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，错误是因为您传递给 loc 的列标签。再看看他们。