keep attrs in xarray.where

doc/whats-new.rst

@@ -22,6 +22,7 @@ v0.17.0 (unreleased)
 
 Breaking changes
 ~~~~~~~~~~~~~~~~
+
 - xarray no longer supports python 3.6
 
   The minimum versions of some other dependencies were changed:
@@ -51,9 +52,11 @@ Deprecations
   version 0.19.0 (:pull:`3993`).
   By `Tom Nicholas <https://github.com/TomNicholas>`_.
 
-
 New Features
 ~~~~~~~~~~~~
+
+- ``keep_attrs`` support for :py:func:`where` (:issue:`4141`, :issue:`4682`, :pull:`4687`).
+  By `Justus Magin <https://github.com/keewis>`_.
 - Xarray now leverages updates as of cftime version 1.4.1, which enable exact I/O
   roundtripping of ``cftime.datetime`` objects (:pull:`4758`).
   By `Spencer Clark <https://github.com/spencerkclark>`_.

xarray/core/computation.py

@@ -1509,6 +1509,10 @@ def where(cond, x, y):
         In priority order: Dataset, DataArray, Variable or array, whichever
         type appears as an input argument.
 
+    Notes
+    -----
+    Only the attrs on `cond` will be kept.
+
     Examples
     --------
     >>> import xarray as xr
@@ -1578,6 +1582,7 @@ def where(cond, x, y):
         join="exact",
         dataset_join="exact",
         dask="allowed",
+        keep_attrs=True,
     )
 
 

xarray/tests/test_computation.py

@@ -1470,6 +1470,13 @@ def test_where():
     assert_identical(expected, actual)
 
 
+def test_where_attrs():
+    cond = xr.DataArray([True, False], dims="x", attrs={"attr": "value"})
+    actual = xr.where(cond, 1, 0)
+    expected = xr.DataArray([1, 0], dims="x", attrs={"attr": "value"})
+    assert_identical(expected, actual)
+
+
 @pytest.mark.parametrize("use_dask", [True, False])
 @pytest.mark.parametrize("use_datetime", [True, False])
 def test_polyval(use_dask, use_datetime):

xarray/tests/test_units.py

@@ -2417,10 +2417,7 @@ def test_binary_operations(self, func, dtype):
         (
             pytest.param(operator.lt, id="less_than"),
             pytest.param(operator.ge, id="greater_equal"),
-            pytest.param(
-                operator.eq,
-                id="equal",
-            ),
+            pytest.param(operator.eq, id="equal"),
         ),
     )
     @pytest.mark.parametrize(