FIX: fix support for single color 2D array as c to mean single color

tacaswell · tacaswell · commit d84f4a7ac8d4 · 2020-05-23T13:00:28.000-04:00
Closes #17423
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -4281,9 +4281,15 @@ def invalid_shape_exception(csize, xsize):
             except ValueError:
                 pass  # Failed to convert to float array; must be color specs.
             else:
+                # handle the documented special case of a 2D array with 1
+                # row which as RGB(A) to broadcast.
+                if c.shape == (1, 4) or c.shape == (1, 3):
+                    c_is_mapped = False
+                    if c.size != xsize:
+                        valid_shape = False
                 # If c can be either mapped values or a RGB(A) color, prefer
                 # the former if shapes match, the latter otherwise.
-                if c.size == xsize:
+                elif c.size == xsize:
                     c = c.ravel()
                     c_is_mapped = True
                 else:  # Wrong size; it must not be intended for mapping.
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -1968,6 +1968,22 @@ def get_next_color():
                     c=c_case, edgecolors="black", kwargs={}, xsize=xsize,
                     get_next_color_func=get_next_color)
 
+    @pytest.mark.style('default')
+    @check_figures_equal(extensions=["png"])
+    def test_scatter_single_color_c(self, fig_test, fig_ref):
+        rgb = [[1, 0.5, 0.05]]
+        rgba = [[1, 0.5, 0.05, .5]]
+
+        # set via color kwarg
+        ax_ref = fig_ref.subplots()
+        ax_ref.scatter(np.ones(3), range(3), color=rgb)
+        ax_ref.scatter(np.ones(4)*2, range(4), color=rgba)
+
+        # set via broadcasting via c
+        ax_test = fig_test.subplots()
+        ax_test.scatter(np.ones(3), range(3), c=rgb)
+        ax_test.scatter(np.ones(4)*2, range(4), c=rgba)
+
 
 def _params(c=None, xsize=2, *, edgecolors=None, **kwargs):
     return (c, edgecolors, kwargs if kwargs is not None else {}, xsize)
