Pandas slicing FutureWarning with 0.21.0

Question

I'm trying to select a subset of a subset of a dataframe, selecting only some columns, and filtering on the rows.

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

However, I'm getting the error:

Passing list-likes to .loc or [] with any missing label will raise

KeyError in the future, you can use .reindex() as an alternative.

What 's the correct way to slice and filter now?

Answer 1

This is a change introduced in v0.21.1,

For example,

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

Try some kind of slicing as you're executing-

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

     A  C

0  7.0  8

2  8.0  7

4  8.0  7

No problem. Now, try substituting C with a non-existent column label -

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 make use of .reindex().

     A   D

0  7.0 NaN

2  8.0 NaN

4  8.0 NaN

So, in your illustration, the error is because of the column labels you pass to loc. Take another look at them.