Add a .drop_attrs method (#8258)

* Add a `.drop_attrs` method

Part of #3891

* Add tests

* Add explicit coords test

* Use `._replace` for half the method

* .

* Add a `deep` kwarg (default `True`?)

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* api

* Update xarray/core/dataarray.py

Co-authored-by: Michael Niklas  <mick.niklas@gmail.com>

* Update xarray/core/dataset.py

Co-authored-by: Michael Niklas  <mick.niklas@gmail.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Michael Niklas <mick.niklas@gmail.com>

Author: 3 people

doc/api.rst

@@ -111,6 +111,7 @@ Dataset contents
    Dataset.drop_duplicates
    Dataset.drop_dims
    Dataset.drop_encoding
+   Dataset.drop_attrs
    Dataset.set_coords
    Dataset.reset_coords
    Dataset.convert_calendar
@@ -306,6 +307,7 @@ DataArray contents
    DataArray.drop_indexes
    DataArray.drop_duplicates
    DataArray.drop_encoding
+   DataArray.drop_attrs
    DataArray.reset_coords
    DataArray.copy
    DataArray.convert_calendar

doc/whats-new.rst

@@ -26,6 +26,10 @@ New Features
   By `Martin Raspaud <https://github.com/mraspaud>`_.
 - Extract the source url from fsspec objects (:issue:`9142`, :pull:`8923`).
   By `Justus Magin <https://github.com/keewis>`_.
+- Add :py:meth:`DataArray.drop_attrs` & :py:meth:`Dataset.drop_attrs` methods,
+  to return an object without ``attrs``. A ``deep`` parameter controls whether
+  variables' ``attrs`` are also dropped.
+  By `Maximilian Roos <https://github.com/max-sixty>`_. (:pull:`8288`)
 
 Breaking changes
 ~~~~~~~~~~~~~~~~

xarray/core/dataarray.py

@@ -7456,3 +7456,20 @@ def to_dask_dataframe(
     # this needs to be at the end, or mypy will confuse with `str`
     # https://mypy.readthedocs.io/en/latest/common_issues.html#dealing-with-conflicting-names
     str = utils.UncachedAccessor(StringAccessor["DataArray"])
+
+    def drop_attrs(self, *, deep: bool = True) -> Self:
+        """
+        Removes all attributes from the DataArray.
+
+        Parameters
+        ----------
+        deep : bool, default True
+            Removes attributes from coordinates.
+
+        Returns
+        -------
+        DataArray
+        """
+        return (
+            self._to_temp_dataset().drop_attrs(deep=deep).pipe(self._from_temp_dataset)
+        )

xarray/core/dataset.py

@@ -10680,3 +10680,45 @@ def resample(
             restore_coord_dims=restore_coord_dims,
             **indexer_kwargs,
         )
+
+    def drop_attrs(self, *, deep: bool = True) -> Self:
+        """
+        Removes all attributes from the Dataset and its variables.
+
+        Parameters
+        ----------
+        deep : bool, default True
+            Removes attributes from all variables.
+
+        Returns
+        -------
+        Dataset
+        """
+        # Remove attributes from the dataset
+        self = self._replace(attrs={})
+
+        if not deep:
+            return self
+
+        # Remove attributes from each variable in the dataset
+        for var in self.variables:
+            # variables don't have a `._replace` method, so we copy and then remove
+            # attrs. If we added a `._replace` method, we could use that instead.
+            if var not in self.indexes:
+                self[var] = self[var].copy()
+                self[var].attrs = {}
+
+        new_idx_variables = {}
+        # Not sure this is the most elegant way of doing this, but it works.
+        # (Should we have a more general "map over all variables, including
+        # indexes" approach?)
+        for idx, idx_vars in self.xindexes.group_by_index():
+            # copy each coordinate variable of an index and drop their attrs
+            temp_idx_variables = {k: v.copy() for k, v in idx_vars.items()}
+            for v in temp_idx_variables.values():
+                v.attrs = {}
+            # re-wrap the index object in new coordinate variables
+            new_idx_variables.update(idx.create_variables(temp_idx_variables))
+        self = self.assign(new_idx_variables)
+
+        return self

xarray/tests/test_dataarray.py

@@ -2980,6 +2980,11 @@ def test_assign_attrs(self) -> None:
         assert_identical(new_actual, expected)
         assert actual.attrs == {"a": 1, "b": 2}
 
+    def test_drop_attrs(self) -> None:
+        # Mostly tested in test_dataset.py, but adding a very small test here
+        da = DataArray([], attrs=dict(a=1, b=2))
+        assert da.drop_attrs().attrs == {}
+
     @pytest.mark.parametrize(
         "func", [lambda x: x.clip(0, 1), lambda x: np.float64(1.0) * x, np.abs, abs]
     )

xarray/tests/test_dataset.py

@@ -4450,6 +4450,54 @@ def test_assign_attrs(self) -> None:
         assert_identical(new_actual, expected)
         assert actual.attrs == dict(a=1, b=2)
 
+    def test_drop_attrs(self) -> None:
+        # Simple example
+        ds = Dataset().assign_attrs(a=1, b=2)
+        original = ds.copy()
+        expected = Dataset()
+        result = ds.drop_attrs()
+        assert_identical(result, expected)
+
+        # Doesn't change original
+        assert_identical(ds, original)
+
+        # Example with variables and coords with attrs, and a multiindex. (arguably
+        # should have used a canonical dataset with all the features we're should
+        # support...)
+        var = Variable("x", [1, 2, 3], attrs=dict(x=1, y=2))
+        idx = IndexVariable("y", [1, 2, 3], attrs=dict(c=1, d=2))
+        mx = xr.Coordinates.from_pandas_multiindex(
+            pd.MultiIndex.from_tuples([(1, 2), (3, 4)], names=["d", "e"]), "z"
+        )
+        ds = Dataset(dict(var1=var), coords=dict(y=idx, z=mx)).assign_attrs(a=1, b=2)
+        assert ds.attrs != {}
+        assert ds["var1"].attrs != {}
+        assert ds["y"].attrs != {}
+        assert ds.coords["y"].attrs != {}
+
+        original = ds.copy(deep=True)
+        result = ds.drop_attrs()
+
+        assert result.attrs == {}
+        assert result["var1"].attrs == {}
+        assert result["y"].attrs == {}
+        assert list(result.data_vars) == list(ds.data_vars)
+        assert list(result.coords) == list(ds.coords)
+
+        # Doesn't change original
+        assert_identical(ds, original)
+        # Specifically test that the attrs on the coords are still there. (The index
+        # can't currently contain `attrs`, so we can't test those.)
+        assert ds.coords["y"].attrs != {}
+
+        # Test for deep=False
+        result_shallow = ds.drop_attrs(deep=False)
+        assert result_shallow.attrs == {}
+        assert result_shallow["var1"].attrs != {}
+        assert result_shallow["y"].attrs != {}
+        assert list(result.data_vars) == list(ds.data_vars)
+        assert list(result.coords) == list(ds.coords)
+
     def test_assign_multiindex_level(self) -> None:
         data = create_test_multiindex()
         with pytest.raises(ValueError, match=r"cannot drop or update.*corrupt.*index "):