Fix incorrect legend labels for Dataset.plot.scatter (#4411)

* Fix incorrect legend labels for Dataset.plot.scatter
Closes #4126

* Update xarray/tests/test_plot.py

Co-authored-by: Deepak Cherian <[email protected]>

Author: phausamann

doc/whats-new.rst

@@ -84,6 +84,8 @@ Bug fixes
 - Fix `KeyError` when doing linear interpolation to an nd `DataArray`
   that contains NaNs (:pull:`4233`).
   By `Jens Svensmark <https://github.com/jenssss>`_
+- Fix incorrect legend labels for :py:meth:`Dataset.plot.scatter` (:issue:`4126`).
+  By `Peter Hausamann <https://github.com/phausamann>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/plot/dataset_plot.py

@@ -339,11 +339,7 @@ def newplotfunc(
             ax.set_ylabel(meta_data.get("ylabel"))
 
         if meta_data["add_legend"]:
-            ax.legend(
-                handles=primitive,
-                labels=list(meta_data["hue"].values),
-                title=meta_data.get("hue_label", None),
-            )
+            ax.legend(handles=primitive, title=meta_data.get("hue_label", None))
         if meta_data["add_colorbar"]:
             cbar_kwargs = {} if cbar_kwargs is None else cbar_kwargs
             if "label" not in cbar_kwargs:

xarray/tests/test_plot.py

@@ -2262,6 +2262,13 @@ def test_non_numeric_legend(self):
         with pytest.raises(ValueError):
             ds2.plot.scatter(x="A", y="B", hue="hue", hue_style="continuous")
 
+    def test_legend_labels(self):
+        # regression test for #4126: incorrect legend labels
+        ds2 = self.ds.copy()
+        ds2["hue"] = ["a", "a", "b", "b"]
+        lines = ds2.plot.scatter(x="A", y="B", hue="hue")
+        assert [t.get_text() for t in lines[0].axes.get_legend().texts] == ["a", "b"]
+
     def test_add_legend_by_default(self):
         sc = self.ds.plot.scatter(x="A", y="B", hue="hue")
         assert len(sc.figure.axes) == 2