Fix Plot with no variance in orient dimension (#3084)

* Fix Plot with no variance in orient dimension

* Update release notes

* Update test with new correct behavior

doc/whatsnew/v0.12.1.rst

@@ -22,6 +22,8 @@ v0.12.1 (Unreleased)
 
 - |Fix| Made :class:`objects.PolyFit` robust to missing data (:pr:`3010`).
 
+- |Fix| Fixed a bug in :class:`objects.Plot` that occurred when the orient coordinate data had zero variance (:pr:`3084`).
+
 - |Fix| Fixed a regression in :func:`kdeplot` where passing `cmap` for an unfilled bivariate plot would raise an exception (:pr:`3065`).
 
 - |Fix| Addressed a performance regression in :func:`lineplot` with a large number of unique x values (:pr:`3081`).

seaborn/_core/scales.py

@@ -94,7 +94,12 @@ def set_default_locators_and_formatters(self, axis):
         return InternalScale(name, (forward, inverse))
 
     def _spacing(self, x: Series) -> float:
-        return self._spacer(x)
+        space = self._spacer(x)
+        if np.isnan(space):
+            # This happens when there is no variance in the orient coordinate data
+            # Not exactly clear what the right default is, but 1 seems reasonable?
+            return 1
+        return space
 
     def _setup(
         self, data: Series, prop: Property, axis: Axis | None = None,

tests/_core/test_plot.py

@@ -683,6 +683,14 @@ def test_empty(self):
         Plot().plot()
         assert m.n_splits == 0
 
+    def test_no_orient_variance(self):
+
+        x, y = [0, 0], [1, 2]
+        m = MockMark()
+        Plot(x, y).add(m).plot()
+        assert_array_equal(m.passed_data[0]["x"], x)
+        assert_array_equal(m.passed_data[0]["y"], y)
+
     def test_single_split_single_layer(self, long_df):
 
         m = MockMark()

tests/_marks/test_line.py

@@ -253,8 +253,9 @@ def test_single_orient_value(self):
         y = [1, 2, 3]
         p = Plot(x, y).add(Lines()).plot()
         lines, = p._figure.axes[0].collections
-        paths, = lines.get_paths()
-        assert paths.vertices.shape == (0, 2)
+        verts = lines.get_paths()[0].vertices.T
+        assert_array_equal(verts[0], x)
+        assert_array_equal(verts[1], y)
 
 
 class TestRange: