diff --git a/xarray/structure/merge.py b/xarray/structure/merge.py
index 7d773ce0b4b..ca1e5ccb2bb 100644
--- a/xarray/structure/merge.py
+++ b/xarray/structure/merge.py
@@ -283,11 +283,17 @@ def merge_collected(
"conflicting attribute values on combined "
f"variable {name!r}:\nfirst value: {variable.attrs!r}\nsecond value: {other_variable.attrs!r}"
)
- merged_vars[name] = variable
- merged_vars[name].attrs = merge_attrs(
+ attrs = merge_attrs(
[var.attrs for var, _ in indexed_elements],
combine_attrs=combine_attrs,
)
+ if variable.attrs or attrs:
+ # Make a shallow copy to so that assigning merged_vars[name].attrs
+ # does not affect the original input variable.
+ merged_vars[name] = variable.copy(deep=False)
+ merged_vars[name].attrs = attrs
+ else:
+ merged_vars[name] = variable
merged_indexes[name] = index
else:
variables = [variable for variable, _ in elements_list]
diff --git a/xarray/tests/test_computation.py b/xarray/tests/test_computation.py
index cb12f3df534..ef9d67b99d6 100644
--- a/xarray/tests/test_computation.py
+++ b/xarray/tests/test_computation.py
@@ -2206,6 +2206,7 @@ def test_where() -> None:
def test_where_attrs() -> None:
cond = xr.DataArray([True, False], coords={"a": [0, 1]}, attrs={"attr": "cond_da"})
cond["a"].attrs = {"attr": "cond_coord"}
+ input_cond = cond.copy()
x = xr.DataArray([1, 1], coords={"a": [0, 1]}, attrs={"attr": "x_da"})
x["a"].attrs = {"attr": "x_coord"}
y = xr.DataArray([0, 0], coords={"a": [0, 1]}, attrs={"attr": "y_da"})
@@ -2216,6 +2217,22 @@ def test_where_attrs() -> None:
expected = xr.DataArray([1, 0], coords={"a": [0, 1]}, attrs={"attr": "x_da"})
expected["a"].attrs = {"attr": "x_coord"}
assert_identical(expected, actual)
+ # Check also that input coordinate attributes weren't modified by reference
+ assert x["a"].attrs == {"attr": "x_coord"}
+ assert y["a"].attrs == {"attr": "y_coord"}
+ assert cond["a"].attrs == {"attr": "cond_coord"}
+ assert_identical(cond, input_cond)
+
+ # 3 DataArrays, drop attrs
+ actual = xr.where(cond, x, y, keep_attrs=False)
+ expected = xr.DataArray([1, 0], coords={"a": [0, 1]})
+ assert_identical(expected, actual)
+ assert_identical(expected.coords["a"], actual.coords["a"])
+ # Check also that input coordinate attributes weren't modified by reference
+ assert x["a"].attrs == {"attr": "x_coord"}
+ assert y["a"].attrs == {"attr": "y_coord"}
+ assert cond["a"].attrs == {"attr": "cond_coord"}
+ assert_identical(cond, input_cond)
# x as a scalar, takes no attrs
actual = xr.where(cond, 0, y, keep_attrs=True)
diff --git a/xarray/tests/test_merge.py b/xarray/tests/test_merge.py
index 302d26df8f3..1b4e1e3e94d 100644
--- a/xarray/tests/test_merge.py
+++ b/xarray/tests/test_merge.py
@@ -183,9 +183,11 @@ def test_merge_arrays_attrs_variables(
self, combine_attrs, attrs1, attrs2, expected_attrs, expect_exception
):
"""check that combine_attrs is used on data variables and coords"""
+ input_attrs1 = attrs1.copy()
data1 = xr.Dataset(
{"var1": ("dim1", [], attrs1)}, coords={"dim1": ("dim1", [], attrs1)}
)
+ input_attrs2 = attrs2.copy()
data2 = xr.Dataset(
{"var1": ("dim1", [], attrs2)}, coords={"dim1": ("dim1", [], attrs2)}
)
@@ -202,6 +204,12 @@ def test_merge_arrays_attrs_variables(
assert_identical(actual, expected)
+ # Check also that input attributes weren't modified
+ assert data1["var1"].attrs == input_attrs1
+ assert data1.coords["dim1"].attrs == input_attrs1
+ assert data2["var1"].attrs == input_attrs2
+ assert data2.coords["dim1"].attrs == input_attrs2
+
def test_merge_attrs_override_copy(self):
ds1 = xr.Dataset(attrs={"x": 0})
ds2 = xr.Dataset(attrs={"x": 1})
@@ -344,6 +352,18 @@ def test_merge(self):
with pytest.raises(ValueError, match=r"should be coordinates or not"):
data.merge(data.reset_coords())
+ def test_merge_drop_attrs(self):
+ data = create_test_data()
+ ds1 = data[["var1"]]
+ ds2 = data[["var3"]]
+ ds1.coords["dim2"].attrs["keep me"] = "example"
+ ds2.coords["numbers"].attrs["foo"] = "bar"
+ actual = ds1.merge(ds2, combine_attrs="drop")
+ assert actual.coords["dim2"].attrs == {}
+ assert actual.coords["numbers"].attrs == {}
+ assert ds1.coords["dim2"].attrs["keep me"] == "example"
+ assert ds2.coords["numbers"].attrs["foo"] == "bar"
+
def test_merge_broadcast_equals(self):
ds1 = xr.Dataset({"x": 0})
ds2 = xr.Dataset({"x": ("y", [0, 0])})
diff --git a/xarray/tests/test_ufuncs.py b/xarray/tests/test_ufuncs.py
index 61cd88e30ac..00d1ed29b32 100644
--- a/xarray/tests/test_ufuncs.py
+++ b/xarray/tests/test_ufuncs.py
@@ -62,6 +62,19 @@ def test_binary_out():
assert_identical(actual_exponent, arg)
+def test_binary_coord_attrs():
+ t = xr.Variable("t", np.arange(2, 4), attrs={"units": "s"})
+ x = xr.DataArray(t.values**2, coords={"t": t}, attrs={"units": "s^2"})
+ y = xr.DataArray(t.values**3, coords={"t": t}, attrs={"units": "s^3"})
+ z1 = xr.apply_ufunc(np.add, x, y, keep_attrs=True)
+ assert z1.coords["t"].attrs == {"units": "s"}
+ z2 = xr.apply_ufunc(np.add, x, y, keep_attrs=False)
+ assert z2.coords["t"].attrs == {}
+ # Check also that input array's coordinate attributes weren't affected
+ assert t.attrs == {"units": "s"}
+ assert x.coords["t"].attrs == {"units": "s"}
+
+
def test_groupby():
ds = xr.Dataset({"a": ("x", [0, 0, 0])}, {"c": ("x", [0, 0, 1])})
ds_grouped = ds.groupby("c")
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