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Fix drop_sel for a MultiIndex #10863

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Merged
merged 9 commits into from
Oct 29, 2025
+22 −1
Merged

Fix drop_sel for a MultiIndex #10863

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d288643
Add test for dropping multiindex labels
owena11 Oct 17, 2025
4eb40ab
Handle DataArray special case for dropping labels
owena11 Oct 17, 2025
7b09905
Merge branch 'main' into 10862_fix_dropsel_multiindex
owena11 Oct 21, 2025
f1089d0
Merge branch 'main' into 10862_fix_dropsel_multiindex
owena11 Oct 23, 2025
22aadff
Merge branch 'main' into 10862_fix_dropsel_multiindex
max-sixty Oct 28, 2025
293fa1f
Validation for DataArray indexing
owena11 Oct 29, 2025
ca372a1
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Oct 29, 2025
7d23fed
Revert "[pre-commit.ci] auto fixes from pre-commit.com hooks"
owena11 Oct 29, 2025
8950155
Revert "Validation for DataArray indexing "
owena11 Oct 29, 2025
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8 changes: 7 additions & 1 deletion xarray/core/dataset.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6065,6 +6065,8 @@ def drop_sel(
Data variables:
A (x, y) int64 32B 0 2 3 5
"""
from xarray.core.dataarray import DataArray
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I've imported DataArray here as that seems to fit with the style in other parts of the codebase (here), however I'm not entirely sure why this is done.

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I think that dataarray.py imports dataset.py already (historically Dataset predates DataArray slightly), so this avoids a recursive import.

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@owena11 owena11 Oct 29, 2025 •
edited
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Great, thanks for the explanation👍


if errors not in ["raise", "ignore"]:
raise ValueError('errors must be either "raise" or "ignore"')

Expand All @@ -6076,7 +6078,11 @@ def drop_sel(
# is a large numpy array
if utils.is_scalar(labels_for_dim):
labels_for_dim = [labels_for_dim]
labels_for_dim = np.asarray(labels_for_dim)
# Most conversion to arrays is better handled in the indexer, however
# DataArrays are a special case where the underlying libraries don't provide
# a good conversition.
if isinstance(labels_for_dim, DataArray):
labels_for_dim = np.asarray(labels_for_dim)
Comment on lines +6081 to +6085
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If you wanted to make this a little safer, could add:

Suggested change
# Most conversion to arrays is better handled in the indexer, however
# DataArrays are a special case where the underlying libraries don't provide
# a good conversition.
if isinstance(labels_for_dim, DataArray):
labels_for_dim = np.asarray(labels_for_dim)
# Most conversion to arrays is better handled in the indexer, however
# DataArrays are a special case where the underlying libraries don't provide
# a good conversition.
if isinstance(labels_for_dim, DataArray):
if labels_for_dim.dims not in ((), (dim,)):
raise ValueError(
"cannot use drop_sel() with DataArray values with "
"along dimensions other than the dimensions being "
f"indexed along: {labels_for_dim}"
)
labels_for_dim = np.asarray(labels_for_dim)

But this LGTM to me! Definitely an incremental improvement.

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Commit and then reverted, highlighed by the tests it might break peoples current usage where a DataArray gets assigned the default dim names (i.e dim_0 etc) .

Also despite thinking this would nudge sel and drop_sel to be more consistent. After checking neither enforcing the alignment between dims for selecting with a DataArray:

>>> data = xr.Dataset({"x": ["a", "b"]})
>>> data.sel(x=xr.DataArray(["a",], dims=("y",)))
<xarray.Dataset> Size: 4B
Dimensions:  (y: 1)
Coordinates:
    x        (y) <U1 4B 'a'
Dimensions without coordinates: y
Data variables:
    *empty*

So would propose leaving this change for now.

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Right, sel() imposes the dimensions and coordinates of the indexer rather than checking for alignment. It is not obvious to me what the inverse of that would be!

try:
index = self.get_index(dim)
except KeyError as err:
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15 changes: 15 additions & 0 deletions xarray/tests/test_dataset.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2980,6 +2980,21 @@ def test_drop_multiindex_level(self) -> None:
actual = data.drop_vars("level_1")
assert_identical(expected, actual)

def test_drop_multiindex_labels(self) -> None:
data = create_test_multiindex()
mindex = pd.MultiIndex.from_tuples(
[
("a", 2),
("b", 1),
("b", 2),
],
names=("level_1", "level_2"),
)
expected = Dataset({}, Coordinates.from_pandas_multiindex(mindex, "x"))

actual = data.drop_sel(x=("a", 1))
assert_identical(expected, actual)

def test_drop_index_labels(self) -> None:
data = Dataset({"A": (["x", "y"], np.random.randn(2, 3)), "x": ["a", "b"]})

Expand Down
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