remove panel conversion (#3845)

Author: max-sixty

doc/whats-new.rst

@@ -95,6 +95,9 @@ Internal Changes
   By `Bruno Pagani <https://github.com/ArchangeGabriel>`_.
 - Updated Azure CI MacOS image, given pending removal.
   By `Maximilian Roos <https://github.com/max-sixty>`_
+- Removed conversion to :py:class:`pandas.Panel`, given its removal in pandas
+  in favor of xarray's objects.
+  By `Maximilian Roos <https://github.com/max-sixty>`_
 
 .. _whats-new.0.15.0:
 

xarray/core/dataarray.py

@@ -2243,20 +2243,14 @@ def to_pandas(self) -> Union["DataArray", pd.Series, pd.DataFrame]:
         * 0D -> `xarray.DataArray`
         * 1D -> `pandas.Series`
         * 2D -> `pandas.DataFrame`
-        * 3D -> `pandas.Panel` *(deprecated)*
 
-        Only works for arrays with 3 or fewer dimensions.
+        Only works for arrays with 2 or fewer dimensions.
 
         The DataArray constructor performs the inverse transformation.
         """
         # TODO: consolidate the info about pandas constructors and the
         # attributes that correspond to their indexes into a separate module?
-        constructors = {
-            0: lambda x: x,
-            1: pd.Series,
-            2: pd.DataFrame,
-            3: pdcompat.Panel,
-        }
+        constructors = {0: lambda x: x, 1: pd.Series, 2: pd.DataFrame}
         try:
             constructor = constructors[self.ndim]
         except KeyError:

xarray/tests/test_dataarray.py

@@ -3411,14 +3411,10 @@ def test_to_pandas(self):
         assert_array_equal(actual.columns, [0, 1])
 
         # roundtrips
-        for shape in [(3,), (3, 4), (3, 4, 5)]:
-            if len(shape) > 2 and LooseVersion(pd.__version__) >= "0.25.0":
-                continue
+        for shape in [(3,), (3, 4)]:
             dims = list("abc")[: len(shape)]
             da = DataArray(np.random.randn(*shape), dims=dims)
-            with warnings.catch_warnings():
-                warnings.filterwarnings("ignore", r"\W*Panel is deprecated")
-                roundtripped = DataArray(da.to_pandas()).drop_vars(dims)
+            roundtripped = DataArray(da.to_pandas()).drop_vars(dims)
             assert_identical(da, roundtripped)
 
         with raises_regex(ValueError, "cannot convert"):