deep copy _indexes (#3899)

doc/whats-new.rst

@@ -39,6 +39,9 @@ New Features
 
 Bug fixes
 ~~~~~~~~~
+- Fix regression where deleting a coordinate from a copied `DataArray` can affect
+  the original `Dataarray`.  (:issue:`3899`, :pull:`3871`)
+  By `Todd Jennings <https://github.com/toddrjen>`_
 
 
 Documentation

xarray/core/dataarray.py

@@ -930,7 +930,10 @@ def copy(self, deep: bool = True, data: Any = None) -> "DataArray":
         """
         variable = self.variable.copy(deep=deep, data=data)
         coords = {k: v.copy(deep=deep) for k, v in self._coords.items()}
-        indexes = self._indexes
+        if self._indexes is None:
+            indexes = self._indexes
+        else:
+            indexes = {k: v.copy(deep=deep) for k, v in self._indexes.items()}
         return self._replace(variable, coords, indexes=indexes)
 
     def __copy__(self) -> "DataArray":

xarray/tests/test_dataarray.py

@@ -4974,3 +4974,28 @@ def test_weakref():
     a = DataArray(1)
     r = ref(a)
     assert r() is a
+
+
+def test_delete_coords():
+    """Make sure that deleting a coordinate doesn't corrupt the DataArray.
+    See issue #3899.
+
+    Also test that deleting succeeds and produces the expected output.
+    """
+    a0 = DataArray(
+        np.array([[1, 2, 3], [4, 5, 6]]),
+        dims=["y", "x"],
+        coords={"x": ["a", "b", "c"], "y": [-1, 1]},
+    )
+    assert_identical(a0, a0)
+
+    a1 = a0.copy()
+    del a1.coords["y"]
+
+    # This test will detect certain sorts of corruption in the DataArray
+    assert_identical(a0, a0)
+
+    assert a0.dims == ("y", "x")
+    assert a1.dims == ("y", "x")
+    assert set(a0.coords.keys()) == {"x", "y"}
+    assert set(a1.coords.keys()) == {"x"}