ENH: Enable using a boolean `loc` in a non-boolean index

[alonme]

Feature Type

• Adding new functionality to pandas

• Changing existing functionality in pandas

• Removing existing functionality in pandas

Problem Description

When using loc to access a boolean value on a DataFrame which has an index that contains both booleans and non-booleans (so the dtype of the index is not bool) an error is raised

import pandas as pd

df = pd.DataFrame({'a': [True, False, "Missing"]}).set_index("a")
df.loc[True]

raises

KeyError: 'True: boolean label can not be used without a boolean index'

I am unsure why this check is performed in _validate_key, but this was an unexpected behavior for me, especially as this works with other combinations of types (int and string for example)

Feature Description

I am not sure why this is currently not supported, so i am unsure if there is a need for a new api or we can use the current one for .loc

Alternative Solutions

df = pd.DataFrame({'a': [True, False, "Missing"]}).set_index("a")
df[df.index == True].loc[True]

This is my current solution, but i don't believe this is a good one

Additional Context

No response

[Rylie-W]

take

[phofl]

@jbrockmendel thoughts here? I am not really sure if this is a good idea since normally Boolean elements are a mask

[jbrockmendel]

I'd expect this to work. The desired behavior seems pretty unambiguous.

[phofl]

If you provide a list of booleans it gets a bit sketchy?

[jbrockmendel]

If you provide a list of booleans it gets a bit sketchy?

Yah. I think in principle we wouldn't allow a mask with .loc.

[Rylie-W]

If you provide a list of booleans it gets a bit sketchy?

Yah. I think in principle we wouldn't allow a mask with .loc.

So in the future, a list of bool elements could be considered as valid for loc only if the index column(s) has one or more bool elements, otherwise it would raise KeyError. And it doesn't check if the length of the list of booleans is the same as the row axis.

Do I understand it right?

[phofl]

Not allowing a mask would force chained indexing though? How would you filter the columns with a mask then?

[jbrockmendel]

Not allowing a mask would force chained indexing though?

Good point. That's a tough one.

Not allowing a mask would force chained indexing though? How would you filter the columns with a mask then?

wouldn't iloc work?

[phofl]

Fair but not ideal I guess for row selection