Merge pull request #17501 from tacaswell/auto-backport-of-pr-17499-on-v3.2.x

tacaswell · web-flow · commit 460805dd56c5 · 2020-05-23T18:21:52.000-04:00
Backport PR #17499: Fix scatter singlecolor
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -4212,19 +4212,26 @@ 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.
                     if c.shape in ((3,), (4,)):
                         _log.warning(
-                            "'c' argument looks like a single numeric RGB or "
+                            "*c* argument looks like a single numeric RGB or "
                             "RGBA sequence, which should be avoided as value-"
                             "mapping will have precedence in case its length "
-                            "matches with 'x' & 'y'.  Please use a 2-D array "
-                            "with a single row if you really want to specify "
+                            "matches with *x* & *y*.  Please use the *color* "
+                            "keyword-argument or provide a 2-D array "
+                            "with a single row if you intend to specify "
                             "the same RGB or RGBA value for all points.")
                     valid_shape = False
         if not c_is_mapped:
@@ -4268,14 +4275,14 @@ def scatter(self, x, y, s=None, c=None, marker=None, cmap=None, norm=None,
             The marker size in points**2.
             Default is ``rcParams['lines.markersize'] ** 2``.
 
-        c : color, sequence, or sequence of colors, optional
-            The marker color. Possible values:
+        c : array-like or list of colors or color, optional
+            The marker colors. Possible values:
 
-            - A single color format string.
-            - A sequence of colors of length n.
             - A scalar or sequence of n numbers to be mapped to colors using
               *cmap* and *norm*.
             - A 2-D array in which the rows are RGB or RGBA.
+            - A sequence of colors of length n.
+            - A single color format string.
 
             Note that *c* should not be a single numeric RGB or RGBA sequence
             because that is indistinguishable from an array of values to be
@@ -4284,9 +4291,12 @@ def scatter(self, x, y, s=None, c=None, marker=None, cmap=None, norm=None,
             matching will have precedence in case of a size matching with *x*
             and *y*.
 
-            Defaults to ``None``. In that case the marker color is determined
-            by the value of ``color``, ``facecolor`` or ``facecolors``. In case
-            those are not specified or ``None``, the marker color is determined
+            If you wish to specify a single color for all points
+            prefer the *color* keyword argument.
+
+            Defaults to `None`. In that case the marker color is determined
+            by the value of *color*, *facecolor* or *facecolors*. In case
+            those are not specified or `None`, the marker color is determined
             by the next color of the ``Axes``' current "shape and fill" color
             cycle. This cycle defaults to :rc:`axes.prop_cycle`.
 
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -2088,6 +2088,22 @@ 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, **kwargs):
     edgecolors = kwargs.pop('edgecolors', None)
