DOC: Should DataFrame.drop() accept a set for the columns , index and labels argument?

[Dr-Irv]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.drop.html

Documentation problem

The arguments labels, index and columns are documented as "single label or list-like". But a set is accepted:

import pandas as pd

df = pd.DataFrame({1: [2], 3: [4]})   # Fix is here
df = df.drop(columns={1})

The pandas source declaration in the typing declarations does not allow a set to be passed.

Suggested fix for documentation

Unclear.

Either we update the docs to say a set is allowed (and update the internal types), OR we add a check to see if a set is passed and raise an exception.

First raised as a pandas-stubs issue in pandas-dev/pandas-stubs#1008

[rhshadrach]

In general, as long as the order is not important for the result, I'm positive on allowing sets. But not strongly so.

[AnuraagaNath]

The original method given by drop via pandas package mentions of the following internal type formats.

(method)
def drop(
    labels: None = ...,
    *,
    axis: Axis = ...,
    index: Hashable | Sequence[Hashable] | Index[Any] = ...,
    columns: Hashable | Sequence[Hashable] | Index[Any],
    level: Level | None = ...,
    inplace: Literal[True],
    errors: IgnoreRaise = ...
) -> None: ...

def drop(
    labels: None = ...,
    *,
    axis: Axis = ...,
    index: Hashable | Sequence[Hashable] | Index[Any],
    columns: Hashable | Sequence[Hashable] | Index[Any] = ...,
    level: Level | None = ...,
    inplace: Literal[True],
    errors: IgnoreRaise = ...
) -> None: ...

def drop(
    labels: Hashable | Sequence[Hashable] | Index[Any],
    *,
    axis: Axis = ...,
    index: None = ...,
    columns: None = ...,
    level: Level | None = ...,
    inplace: Literal[True],
    errors: IgnoreRaise = ...
) -> None: ...

def drop(
    labels: None = ...,
    *,
    axis: Axis = ...,
    index: Hashable | Sequence[Hashable] | Index[Any] = ...,
    columns: Hashable | Sequence[Hashable] | Index[Any],
    level: Level | None = ...,
    inplace: Literal[False] = ...,
    errors: IgnoreRaise = ...
) -> DataFrame: ...

def drop(
    labels: None = ...,
    *,
    axis: Axis = ...,
    index: Hashable | Sequence[Hashable] | Index[Any],
    columns: Hashable | Sequence[Hashable] | Index[Any] = ...,
    level: Level | None = ...,
    inplace: Literal[False] = ...,
    errors: IgnoreRaise = ...
) -> DataFrame: ...

def drop(
    labels: Hashable | Sequence[Hashable] | Index[Any],
    *,
    axis: Axis = ...,
    index: None = ...,
    columns: None = ...,
    level: Level | None = ...,
    inplace: Literal[False] = ...,
    errors: IgnoreRaise = ...
) -> DataFrame: ...

def drop(
    labels: None = ...,
    *,
    axis: Axis = ...,
    index: Hashable | Sequence[Hashable] | Index[Any] = ...,
    columns: Hashable | Sequence[Hashable] | Index[Any],
    level: Level | None = ...,
    inplace: _bool = ...,
    errors: IgnoreRaise = ...
) -> (DataFrame | None): ...

def drop(
    labels: None = ...,
    *,
    axis: Axis = ...,
    index: Hashable | Sequence[Hashable] | Index[Any],
    columns: Hashable | Sequence[Hashable] | Index[Any] = ...,
    level: Level | None = ...,
    inplace: _bool = ...,
    errors: IgnoreRaise = ...
) -> (DataFrame | None): ...

def drop(
    labels: Hashable | Sequence[Hashable] | Index[Any],
    *,
    axis: Axis = ...,
    index: None = ...,
    columns: None = ...,
    level: Level | None = ...,
    inplace: _bool = ...,
    errors: IgnoreRaise = ...
) -> (DataFrame | None): ...

drop function supports this many combination of types during operations. All the functions are same. Documentation is less descriptive about this thing.

[Dr-Irv]

drop function supports this many combination of types during operations. All the functions are same. Documentation is less descriptive about this thing.

yes and no. The type declarations for any of index, columns and labels are all allowing any of these:

• A single Hashable
• A sequence of Hashable
• An Index

The docs currently say "single label or list-like" for those 3. A set is not "list-like", nor would a set pass those type declarations.

But at runtime, a set is supported. So the question is whether we change the type declarations and the docs, OR do we disallow a set at runtime (since the type declarations already disallow it).

[cmp0xff]

In the specific case of labels in drop, I think using a set or, in general, collections.abc.Collection is fine, since the result should not depend on the order of the labels. Maybe even collections.abc.Iterable should be fine.