From 615b878f937160da6566f314872fb8b1d81d07cc Mon Sep 17 00:00:00 2001
From: NoiceHax <yashasprakash021@gmail.com>
Date: Sat, 15 Aug 2026 15:06:58 +0530
Subject: [PATCH] fix: accept sets in isin

numpy turns a set into a 0d object array, so Dataset.isin and
DataArray.isin returned False everywhere when given a set. Convert
set-like arguments to a list before handing them to numpy.

Co-authored-by: Claude <noreply@anthropic.com>
---
 doc/whats-new.rst              | 5 +++++
 xarray/core/common.py          | 7 +++++++
 xarray/tests/test_dataarray.py | 7 +++++++
 xarray/tests/test_dataset.py   | 5 ++++-
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 0e74ca1e2fc..70ec89f96c9 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -69,6 +69,11 @@ Bug Fixes
   for zarr writes. Existing zarr stores written with the old ``int8`` encoding
   are still read correctly. (:issue:`2937`, :pull:`11318`)
   By `Evan Lyall <https://github.com/elyall>`_.
+- :py:meth:`~xarray.DataArray.isin` and :py:meth:`~xarray.Dataset.isin` now
+  accept sets, frozensets and other set-like objects such as ``dict.keys()``.
+  Previously these were turned into a 0-dimensional object array by numpy, so
+  the result was ``False`` everywhere (:issue:`10022`).
+  By `Chandan P <https://github.com/NoiceHax>`_.
 
 
 Documentation
diff --git a/xarray/core/common.py b/xarray/core/common.py
index 4c506b05325..6d803ea4fd3 100644
--- a/xarray/core/common.py
+++ b/xarray/core/common.py
@@ -3,6 +3,7 @@
 import datetime
 import warnings
 from collections.abc import Callable, Hashable, Iterable, Iterator, Mapping
+from collections.abc import Set as AbstractSet
 from contextlib import suppress
 from html import escape
 from textwrap import dedent
@@ -1366,6 +1367,8 @@ def isin(self, test_elements: Any) -> Self:
         test_elements : array_like
             The values against which to test each value of `element`.
             This argument is flattened if an array or array_like.
+            Sets (and other set-like objects such as ``dict.keys()``) are
+            converted to a list first.
             See numpy notes for behavior with non-array-like parameters.
 
         Returns
@@ -1394,6 +1397,10 @@ def isin(self, test_elements: Any) -> Self:
             raise TypeError(
                 f"isin() argument must be convertible to an array: {test_elements}"
             )
+        elif isinstance(test_elements, AbstractSet):
+            # numpy converts a set to a 0d object array, which never compares
+            # equal to any element, so convert it to a sequence first
+            test_elements = list(test_elements)
         elif isinstance(test_elements, Variable | DataArray):
             # need to explicitly pull out data to support dask arrays as the
             # second argument
diff --git a/xarray/tests/test_dataarray.py b/xarray/tests/test_dataarray.py
index b2619008379..fe5b4fe6b31 100644
--- a/xarray/tests/test_dataarray.py
+++ b/xarray/tests/test_dataarray.py
@@ -7018,6 +7018,13 @@ def test_isin(da) -> None:
     result = da.isin([2, 3]).sel(y=list("de"), z=0)
     assert_equal(result, expected)
 
+    # set-like objects give the same answer as the equivalent list, GH10022
+    result = da.isin({2, 3}).sel(y=list("de"), z=0)
+    assert_equal(result, expected)
+
+    result = da.isin({2: "a", 3: "b"}.keys()).sel(y=list("de"), z=0)
+    assert_equal(result, expected)
+
 
 def test_raise_no_warning_for_nan_in_binary_ops() -> None:
     with assert_no_warnings():
diff --git a/xarray/tests/test_dataset.py b/xarray/tests/test_dataset.py
index a7178bba512..c3574c979af 100644
--- a/xarray/tests/test_dataset.py
+++ b/xarray/tests/test_dataset.py
@@ -7815,7 +7815,10 @@ def test_query(self, backend, engine, parser) -> None:
 # pytest tests — new tests should go here, rather than in the class.
 
 
-@pytest.mark.parametrize("test_elements", ([1, 2], np.array([1, 2]), DataArray([1, 2])))
+@pytest.mark.parametrize(
+    "test_elements",
+    ([1, 2], np.array([1, 2]), DataArray([1, 2]), {1, 2}, frozenset({1, 2})),
+)
 def test_isin(test_elements, backend) -> None:
     expected = Dataset(
         data_vars={