Preserve attrs with coarsen

.pre-commit-config.yaml

@@ -6,7 +6,7 @@ repos:
     hooks:
       - id: isort
   # https://github.com/python/black#version-control-integration
-  - repo: https://github.com/python/black
+  - repo: https://github.com/psf/black
     rev: 20.8b1
     hooks:
       - id: black

doc/whats-new.rst

@@ -77,6 +77,7 @@ Bug fixes
   and :py:meth:`DataArray.str.wrap` (:issue:`4334`). By `Mathias Hauser <https://github.com/mathause>`_.
 - Fixed overflow issue causing incorrect results in computing means of :py:class:`cftime.datetime`
   arrays (:issue:`4341`). By `Spencer Clark <https://github.com/spencerkclark>`_.
+- Fixed :py:meth:`Dataset.coarsen`, :py:meth:`DataArray.coarsen` dropping attributes on original object (:issue:`4120`, :pull:`4360`). by `Julia Kent <https://github.com/jukent>`_.
 - fix the signature of the plot methods. (:pull:`4359`) By `Justus Magin <https://github.com/keewis>`_.
 - Fix :py:func:`xarray.apply_ufunc` with ``vectorize=True`` and ``exclude_dims`` (:issue:`3890`).
   By `Mathias Hauser <https://github.com/mathause>`_.

xarray/core/rolling.py

@@ -690,7 +690,7 @@ def wrapped_func(self, **kwargs):
             from .dataarray import DataArray
 
             reduced = self.obj.variable.coarsen(
-                self.windows, func, self.boundary, self.side, **kwargs
+                self.windows, func, self.boundary, self.side, self.keep_attrs, **kwargs
             )
             coords = {}
             for c, v in self.obj.coords.items():
@@ -703,6 +703,7 @@ def wrapped_func(self, **kwargs):
                             self.coord_func[c],
                             self.boundary,
                             self.side,
+                            self.keep_attrs,
                             **kwargs,
                         )
                     else:

xarray/core/variable.py

@@ -1993,21 +1993,32 @@ def rolling_window(
             ),
         )
 
-    def coarsen(self, windows, func, boundary="exact", side="left", **kwargs):
+    def coarsen(
+        self, windows, func, boundary="exact", side="left", keep_attrs=None, **kwargs
+    ):
         """
         Apply reduction function.
         """
         windows = {k: v for k, v in windows.items() if k in self.dims}
         if not windows:
             return self.copy()
 
+        if keep_attrs is None:
+            keep_attrs = _get_keep_attrs(default=False)
+
+        if keep_attrs:
+            _attrs = self.attrs
+        else:
+            _attrs = None
+
         reshaped, axes = self._coarsen_reshape(windows, boundary, side)
         if isinstance(func, str):
             name = func
             func = getattr(duck_array_ops, name, None)
             if func is None:
                 raise NameError(f"{name} is not a valid method.")
-        return self._replace(data=func(reshaped, axis=axes, **kwargs))
+
+        return self._replace(data=func(reshaped, axis=axes, **kwargs), attrs=_attrs)
 
     def _coarsen_reshape(self, windows, boundary, side):
         """
@@ -2072,9 +2083,6 @@ def _coarsen_reshape(self, windows, boundary, side):
             else:
                 shape.append(variable.shape[i])
 
-        keep_attrs = _get_keep_attrs(default=False)
-        variable.attrs = variable._attrs if keep_attrs else {}
-
         return variable.data.reshape(shape), tuple(axes)
 
     @property

xarray/tests/test_dataarray.py

@@ -6186,6 +6186,35 @@ def test_isin(da):
     assert_equal(result, expected)
 
 
+def test_coarsen_keep_attrs():
+    _attrs = {"units": "test", "long_name": "testing"}
+
+    da = xr.DataArray(
+        np.linspace(0, 364, num=364),
+        dims="time",
+        coords={"time": pd.date_range("15/12/1999", periods=364)},
+        attrs=_attrs,
+    )
+
+    da2 = da.copy(deep=True)
+
+    # Test dropped attrs
+    dat = da.coarsen(time=3, boundary="trim").mean()
+    assert dat.attrs == {}
+
+    # Test kept attrs using dataset keyword
+    dat = da.coarsen(time=3, boundary="trim", keep_attrs=True).mean()
+    assert dat.attrs == _attrs
+
+    # Test kept attrs using global option
+    with xr.set_options(keep_attrs=True):
+        dat = da.coarsen(time=3, boundary="trim").mean()
+    assert dat.attrs == _attrs
+
+    # Test kept attrs in original object
+    xr.testing.assert_identical(da, da2)
+
+
 @pytest.mark.filterwarnings("error:Mean of empty slice")
 @pytest.mark.parametrize("da", (1, 2), indirect=True)
 def test_rolling_iter(da):

xarray/tests/test_dataset.py

@@ -5956,6 +5956,8 @@ def test_coarsen_keep_attrs():
         attrs=_attrs,
     )
 
+    ds2 = ds.copy(deep=True)
+
     # Test dropped attrs
     dat = ds.coarsen(coord=5).mean()
     assert dat.attrs == {}
@@ -5969,6 +5971,9 @@ def test_coarsen_keep_attrs():
         dat = ds.coarsen(coord=5).mean()
     assert dat.attrs == _attrs
 
+    # Test kept attrs in original object
+    xr.testing.assert_identical(ds, ds2)
+
 
 def test_rolling_keep_attrs():
     _attrs = {"units": "test", "long_name": "testing"}

xarray/tests/test_variable.py

@@ -1949,7 +1949,10 @@ def test_coarsen_keep_attrs(self, operation="mean"):
         # Test kept attrs
         with set_options(keep_attrs=True):
             new = Variable(["coord"], np.linspace(1, 10, 100), attrs=_attrs).coarsen(
-                windows={"coord": 1}, func=test_func, boundary="exact", side="left"
+                windows={"coord": 1},
+                func=test_func,
+                boundary="exact",
+                side="left",
             )
         assert new.attrs == _attrs