Fix Dataset/DataArray.isel with drop=True and scalar DataArray indexes

doc/whats-new.rst

@@ -119,6 +119,9 @@ Bug fixes
   :pull:`6489`). By `Spencer Clark <https://github.com/spencerkclark>`_.
 - Dark themes are now properly detected in Furo-themed Sphinx documents (:issue:`6500`, :pull:`6501`).
   By `Kevin Paul <https://github.com/kmpaul>`_.
+- :py:meth:`isel` with `drop=True` works as intended with scalar :py:class:`DataArray` indexers.
+  (:issue:`6554`, :pull:`6579`)
+  By `Michael Niklas <https://github.com/headtr1ck>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/dataarray.py

@@ -77,7 +77,7 @@
     except ImportError:
         iris_Cube = None
 
-    from .types import T_DataArray, T_Xarray
+    from .types import ErrorChoice, ErrorChoiceWithWarn, T_DataArray, T_Xarray
 
 
 def _infer_coords_and_dims(
@@ -1170,7 +1170,7 @@ def isel(
         self,
         indexers: Mapping[Any, Any] = None,
         drop: bool = False,
-        missing_dims: str = "raise",
+        missing_dims: ErrorChoiceWithWarn = "raise",
         **indexers_kwargs: Any,
     ) -> DataArray:
         """Return a new DataArray whose data is given by integer indexing
@@ -1185,7 +1185,7 @@ def isel(
             If DataArrays are passed as indexers, xarray-style indexing will be
             carried out. See :ref:`indexing` for the details.
             One of indexers or indexers_kwargs must be provided.
-        drop : bool, optional
+        drop : bool, default False
             If ``drop=True``, drop coordinates variables indexed by integers
             instead of making them scalar.
         missing_dims : {"raise", "warn", "ignore"}, default: "raise"
@@ -2385,7 +2385,7 @@ def T(self) -> DataArray:
         return self.transpose()
 
     def drop_vars(
-        self, names: Hashable | Iterable[Hashable], *, errors: str = "raise"
+        self, names: Hashable | Iterable[Hashable], *, errors: ErrorChoice = "raise"
     ) -> DataArray:
         """Returns an array with dropped variables.
 
@@ -4586,7 +4586,7 @@ def query(
         queries: Mapping[Any, Any] = None,
         parser: str = "pandas",
         engine: str = None,
-        missing_dims: str = "raise",
+        missing_dims: ErrorChoiceWithWarn = "raise",
         **queries_kwargs: Any,
     ) -> DataArray:
         """Return a new data array indexed along the specified

xarray/core/dataset.py

@@ -105,7 +105,7 @@
     from ..backends import AbstractDataStore, ZarrStore
     from .dataarray import DataArray
     from .merge import CoercibleMapping
-    from .types import T_Xarray
+    from .types import ErrorChoiceWithWarn, T_Xarray
 
     try:
         from dask.delayed import Delayed
@@ -2163,7 +2163,7 @@ def isel(
         self,
         indexers: Mapping[Any, Any] = None,
         drop: bool = False,
-        missing_dims: str = "raise",
+        missing_dims: ErrorChoiceWithWarn = "raise",
         **indexers_kwargs: Any,
     ) -> Dataset:
         """Returns a new dataset with each array indexed along the specified
@@ -2182,14 +2182,14 @@ def isel(
             If DataArrays are passed as indexers, xarray-style indexing will be
             carried out. See :ref:`indexing` for the details.
             One of indexers or indexers_kwargs must be provided.
-        drop : bool, optional
+        drop : bool, default False
             If ``drop=True``, drop coordinates variables indexed by integers
             instead of making them scalar.
         missing_dims : {"raise", "warn", "ignore"}, default: "raise"
             What to do if dimensions that should be selected from are not present in the
             Dataset:
             - "raise": raise an exception
-            - "warning": raise a warning, and ignore the missing dimensions
+            - "warn": raise a warning, and ignore the missing dimensions
             - "ignore": ignore the missing dimensions
         **indexers_kwargs : {dim: indexer, ...}, optional
             The keyword arguments form of ``indexers``.
@@ -2254,7 +2254,7 @@ def _isel_fancy(
         indexers: Mapping[Any, Any],
         *,
         drop: bool,
-        missing_dims: str = "raise",
+        missing_dims: ErrorChoiceWithWarn = "raise",
     ) -> Dataset:
         valid_indexers = dict(self._validate_indexers(indexers, missing_dims))
 
@@ -2270,6 +2270,8 @@ def _isel_fancy(
                 }
                 if var_indexers:
                     new_var = var.isel(indexers=var_indexers)
+                    if drop and new_var.ndim == 0:
+                        continue
                 else:
                     new_var = var.copy(deep=False)
                 if name not in indexes:
@@ -7713,7 +7715,7 @@ def query(
         queries: Mapping[Any, Any] = None,
         parser: str = "pandas",
         engine: str = None,
-        missing_dims: str = "raise",
+        missing_dims: ErrorChoiceWithWarn = "raise",
         **queries_kwargs: Any,
     ) -> Dataset:
         """Return a new dataset with each array indexed along the specified
@@ -7746,7 +7748,7 @@ def query(
             Dataset:
 
             - "raise": raise an exception
-            - "warning": raise a warning, and ignore the missing dimensions
+            - "warn": raise a warning, and ignore the missing dimensions
             - "ignore": ignore the missing dimensions
 
         **queries_kwargs : {dim: query, ...}, optional

xarray/core/types.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, TypeVar, Union
+from typing import TYPE_CHECKING, Literal, TypeVar, Union
 
 import numpy as np
 
@@ -33,3 +33,6 @@
 DaCompatible = Union["DataArray", "Variable", "DataArrayGroupBy", "ScalarOrArray"]
 VarCompatible = Union["Variable", "ScalarOrArray"]
 GroupByIncompatible = Union["Variable", "GroupBy"]
+
+ErrorChoice = Literal["raise", "ignore"]
+ErrorChoiceWithWarn = Literal["raise", "warn", "ignore"]

xarray/tests/test_dataset.py

@@ -1175,6 +1175,17 @@ def test_isel_fancy(self):
         assert_array_equal(actual["var2"], expected_var2)
         assert_array_equal(actual["var3"], expected_var3)
 
+        # test that drop works
+        ds = xr.Dataset({"a": (("x",), [1, 2, 3])}, coords={"b": (("x",), [5, 6, 7])})
+
+        actual = ds.isel({"x": 1}, drop=False)
+        expected = xr.Dataset({"a": 2}, coords={"b": 6})
+        assert_identical(actual, expected)
+
+        actual = ds.isel({"x": 1}, drop=True)
+        expected = xr.Dataset({"a": 2})
+        assert_identical(actual, expected)
+
     def test_isel_dataarray(self):
         """Test for indexing by DataArray"""
         data = create_test_data()