Allow swap_dims to take kwargs (#4841)

doc/whats-new.rst

@@ -46,7 +46,10 @@ Breaking changes
 New Features
 ~~~~~~~~~~~~
 - Performance improvement when constructing DataArrays. Significantly speeds up repr for Datasets with large number of variables.
-  By `Deepak Cherian <https://github.com/dcherian>`_
+  By `Deepak Cherian <https://github.com/dcherian>`_.
+- :py:meth:`DataArray.swap_dims` & :py:meth:`Dataset.swap_dims` now accept dims
+  in the form of kwargs as well as a dict, like most similar methods.
+  By `Maximilian Roos <https://github.com/max-sixty>`_.
 
 Bug fixes
 ~~~~~~~~~

xarray/core/dataarray.py

@@ -1699,7 +1699,9 @@ def rename(
             new_name_or_name_dict = cast(Hashable, new_name_or_name_dict)
             return self._replace(name=new_name_or_name_dict)
 
-    def swap_dims(self, dims_dict: Mapping[Hashable, Hashable]) -> "DataArray":
+    def swap_dims(
+        self, dims_dict: Mapping[Hashable, Hashable] = None, **dims_kwargs
+    ) -> "DataArray":
         """Returns a new DataArray with swapped dimensions.
 
         Parameters
@@ -1708,6 +1710,10 @@ def swap_dims(self, dims_dict: Mapping[Hashable, Hashable]) -> "DataArray":
             Dictionary whose keys are current dimension names and whose values
             are new names.
 
+        **dim_kwargs : {dim: , ...}, optional
+            The keyword arguments form of ``dims_dict``.
+            One of dims_dict or dims_kwargs must be provided.
+
         Returns
         -------
         swapped : DataArray
@@ -1749,6 +1755,7 @@ def swap_dims(self, dims_dict: Mapping[Hashable, Hashable]) -> "DataArray":
         DataArray.rename
         Dataset.swap_dims
         """
+        dims_dict = either_dict_or_kwargs(dims_dict, dims_kwargs, "swap_dims")
         ds = self._to_temp_dataset().swap_dims(dims_dict)
         return self._from_temp_dataset(ds)
 

xarray/core/dataset.py

@@ -3155,7 +3155,9 @@ def rename_vars(
         )
         return self._replace(variables, coord_names, dims=dims, indexes=indexes)
 
-    def swap_dims(self, dims_dict: Mapping[Hashable, Hashable]) -> "Dataset":
+    def swap_dims(
+        self, dims_dict: Mapping[Hashable, Hashable] = None, **dims_kwargs
+    ) -> "Dataset":
         """Returns a new object with swapped dimensions.
 
         Parameters
@@ -3164,6 +3166,10 @@ def swap_dims(self, dims_dict: Mapping[Hashable, Hashable]) -> "Dataset":
             Dictionary whose keys are current dimension names and whose values
             are new names.
 
+        **dim_kwargs : {existing_dim: new_dim, ...}, optional
+            The keyword arguments form of ``dims_dict``.
+            One of dims_dict or dims_kwargs must be provided.
+
         Returns
         -------
         swapped : Dataset
@@ -3214,6 +3220,8 @@ def swap_dims(self, dims_dict: Mapping[Hashable, Hashable]) -> "Dataset":
         """
         # TODO: deprecate this method in favor of a (less confusing)
         # rename_dims() method that only renames dimensions.
+
+        dims_dict = either_dict_or_kwargs(dims_dict, dims_kwargs, "swap_dims")
         for k, v in dims_dict.items():
             if k not in self.dims:
                 raise ValueError(

xarray/tests/test_dataarray.py

@@ -1639,6 +1639,16 @@ def test_swap_dims(self):
                 expected.indexes[dim_name], actual.indexes[dim_name]
             )
 
+        # as kwargs
+        array = DataArray(np.random.randn(3), {"x": list("abc")}, "x")
+        expected = DataArray(array.values, {"x": ("y", list("abc"))}, dims="y")
+        actual = array.swap_dims(x="y")
+        assert_identical(expected, actual)
+        for dim_name in set().union(expected.indexes.keys(), actual.indexes.keys()):
+            pd.testing.assert_index_equal(
+                expected.indexes[dim_name], actual.indexes[dim_name]
+            )
+
         # multiindex case
         idx = pd.MultiIndex.from_arrays([list("aab"), list("yzz")], names=["y1", "y2"])
         array = DataArray(np.random.randn(3), {"y": ("x", idx)}, "x")

xarray/tests/test_dataset.py

@@ -2748,6 +2748,13 @@ def test_swap_dims(self):
         actual = original.swap_dims({"x": "u"})
         assert_identical(expected, actual)
 
+        # as kwargs
+        expected = Dataset(
+            {"y": ("u", list("abc")), "z": 42}, coords={"x": ("u", [1, 2, 3])}
+        )
+        actual = original.swap_dims(x="u")
+        assert_identical(expected, actual)
+
         # handle multiindex case
         idx = pd.MultiIndex.from_arrays([list("aab"), list("yzz")], names=["y1", "y2"])
         original = Dataset({"x": [1, 2, 3], "y": ("x", idx), "z": 42})