improve markers distribution by using averages of values next to nans

rc · rc · commit 3a3d52ce3cc7 · 2022-02-22T13:15:11.000+01:00
diff --git a/lib/matplotlib/lines.py b/lib/matplotlib/lines.py
@@ -159,8 +159,23 @@ def _slice_or_none(in_v, slc):
                     "markevery is specified relative to the axes size, but "
                     "the line does not have a Axes as parent")
             # calc cumulative distance along path (in display coords):
-            aux = np.where(np.isfinite(tpath.vertices), tpath.vertices,
-                           np.nanmean(tpath.vertices, axis=0))
+            mask = np.isnan(tpath.vertices)
+            if mask.any():
+                aux = np.empty_like(tpath.vertices)
+                for ic, vals in enumerate(tpath.vertices.T):
+                    ok = ~mask[:, ic]
+                    ii = np.where(ok, np.arange(ok.shape[0]), -1)
+                    i0, i1 = np.nonzero(ok)[0][[0, -1]]
+                    ii[:i0] = i0
+                    ilo = np.maximum.accumulate(ii)
+                    ii[mask[:, ic]] = ok.shape[0] - 1
+                    ii[i1:] = i1
+                    ihi = np.minimum.accumulate(ii[::-1])[::-1]
+                    aux[:, ic] = 0.5 * (vals[ilo] + vals[ihi])
+
+            else:
+                aux = tpath.vertices
+
             disp_coords = affine.transform(aux)
             delta = np.empty((len(disp_coords), 2))
             delta[0, :] = 0
