Remove hue_style from plot1d docstring (#7925)

* Remove hue_style from plot1d docstring

* Add deprecation warning

* Remove  hue_style in scatter tests

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

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

* hmm timedelta is numeric?

* Update utils.py

* Update test_plot.py

* Update whats-new.rst

* fix merge errors

---------

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

doc/whats-new.rst

@@ -29,7 +29,8 @@ Breaking changes
 
 Deprecations
 ~~~~~~~~~~~~
-
+- `hue_style` is being deprecated for scatter plots. (:issue:`7907`, :pull:`7925`).
+  By `Jimmy Westling <https://github.com/illviljan>`_.
 
 Bug fixes
 ~~~~~~~~~
@@ -43,8 +44,6 @@ Internal Changes
 ~~~~~~~~~~~~~~~~
 
 
-.. _whats-new.2023.07.0:
-
 v2023.07.0 (July 11, 2023)
 --------------------------
 

xarray/plot/dataarray_plot.py

@@ -733,15 +733,6 @@ def _plot1d(plotfunc):
         If specified plot 3D and use this coordinate for *z* axis.
     hue : Hashable or None, optional
         Dimension or coordinate for which you want multiple lines plotted.
-    hue_style: {'discrete', 'continuous'} or None, optional
-        How to use the ``hue`` variable:
-
-        - ``'continuous'`` -- continuous color scale
-          (default for numeric ``hue`` variables)
-        - ``'discrete'`` -- a color for each unique value,
-          using the default color cycle
-          (default for non-numeric ``hue`` variables)
-
     markersize: Hashable or None, optional
         scatter only. Variable by which to vary size of scattered points.
     linewidth: Hashable or None, optional
@@ -935,6 +926,19 @@ def newplotfunc(
                 warnings.warn(msg, DeprecationWarning, stacklevel=2)
         del args
 
+        if hue_style is not None:
+            # TODO: Not used since 2022.10. Deprecated since 2023.07.
+            warnings.warn(
+                (
+                    "hue_style is no longer used for plot1d plots "
+                    "and the argument will eventually be removed. "
+                    "Convert numbers to string for a discrete hue "
+                    "and use add_legend or add_colorbar to control which guide to display."
+                ),
+                DeprecationWarning,
+                stacklevel=2,
+            )
+
         _is_facetgrid = kwargs.pop("_is_facetgrid", False)
 
         if plotfunc.__name__ == "scatter":

xarray/plot/utils.py

@@ -1438,6 +1438,16 @@ def data_is_numeric(self) -> bool:
         >>> a = xr.DataArray([0.5, 0, 0, 0.5, 2, 3])
         >>> _Normalize(a).data_is_numeric
         True
+
+        >>> # TODO: Datetime should be numeric right?
+        >>> a = xr.DataArray(pd.date_range("2000-1-1", periods=4))
+        >>> _Normalize(a).data_is_numeric
+        False
+
+        # TODO: Timedelta should be numeric right?
+        >>> a = xr.DataArray(pd.timedelta_range("-1D", periods=4, freq="D"))
+        >>> _Normalize(a).data_is_numeric
+        True
         """
         return self._data_is_numeric
 

xarray/tests/test_plot.py

@@ -2708,23 +2708,32 @@ def test_bad_args(
                 x=x, y=y, hue=hue, add_legend=add_legend, add_colorbar=add_colorbar
             )
 
-    @pytest.mark.xfail(reason="datetime,timedelta hue variable not supported.")
-    @pytest.mark.parametrize("hue_style", ["discrete", "continuous"])
-    def test_datetime_hue(self, hue_style: Literal["discrete", "continuous"]) -> None:
+    def test_datetime_hue(self) -> None:
         ds2 = self.ds.copy()
+
+        # TODO: Currently plots as categorical, should it behave as numerical?
         ds2["hue"] = pd.date_range("2000-1-1", periods=4)
-        ds2.plot.scatter(x="A", y="B", hue="hue", hue_style=hue_style)
+        ds2.plot.scatter(x="A", y="B", hue="hue")
 
         ds2["hue"] = pd.timedelta_range("-1D", periods=4, freq="D")
-        ds2.plot.scatter(x="A", y="B", hue="hue", hue_style=hue_style)
+        ds2.plot.scatter(x="A", y="B", hue="hue")
 
-    @pytest.mark.parametrize("hue_style", ["discrete", "continuous"])
-    def test_facetgrid_hue_style(
-        self, hue_style: Literal["discrete", "continuous"]
-    ) -> None:
-        g = self.ds.plot.scatter(
-            x="A", y="B", row="row", col="col", hue="hue", hue_style=hue_style
-        )
+    def test_facetgrid_hue_style(self) -> None:
+        ds2 = self.ds.copy()
+
+        # Numbers plots as continous:
+        g = ds2.plot.scatter(x="A", y="B", row="row", col="col", hue="hue")
+        assert isinstance(g._mappables[-1], mpl.collections.PathCollection)
+
+        # Datetimes plots as categorical:
+        # TODO: Currently plots as categorical, should it behave as numerical?
+        ds2["hue"] = pd.date_range("2000-1-1", periods=4)
+        g = ds2.plot.scatter(x="A", y="B", row="row", col="col", hue="hue")
+        assert isinstance(g._mappables[-1], mpl.collections.PathCollection)
+
+        # Strings plots as categorical:
+        ds2["hue"] = ["a", "a", "b", "b"]
+        g = ds2.plot.scatter(x="A", y="B", row="row", col="col", hue="hue")
         assert isinstance(g._mappables[-1], mpl.collections.PathCollection)
 
     @pytest.mark.parametrize(