bugfix for #8818

zhangeugenia · zhangeugenia · commit 1f8bad291ca0 · 2018-03-16T03:14:12.000-04:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -55,22 +55,24 @@ def _plot_args_replacer(args, data):
         return ["y"]
     elif len(args) == 2:
         # this can be two cases: x,y or y,c
-        if not args[1] in data:
-            # this is not in data, so just assume that it is something which
-            # will not get replaced (color spec or array like).
-            return ["y", "c"]
         # it's data, but could be a color code like 'ro' or 'b--'
         # -> warn the user in that case...
+
         try:
             _process_plot_format(args[1])
         except ValueError:
             pass
         else:
-            warnings.warn(
-                "Second argument {!r} is ambiguous: could be a color spec but "
-                "is in data; using as data.  Either rename the entry in data "
-                "or use three arguments to plot.".format(args[1]),
-                RuntimeWarning, stacklevel=3)
+            # arg can be parsed into colour; verify arg is not data
+            if not args[1] in data:
+                return ["y", "c"]
+            else:
+                warnings.warn(
+                    "Second argument {!r} is ambiguous: could be a color spec but "
+                    "is in data; using as data.  Either rename the entry in data "
+                    "or use three arguments to plot.".format(args[1]),
+                    RuntimeWarning, stacklevel=3)
+
         return ["x", "y"]
     elif len(args) == 3:
         return ["x", "y", "c"]
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -584,6 +584,15 @@ def test_shaped_data():
     plt.plot(xdata[:, 1], xdata[1, :], 'o')
 
 
+def test_structured_data():
+    # support for stuctured data
+    pts = np.array([(1, 1), (2, 2)], dtype=[("ones", float), ("twos", float)])
+
+    fig, ax = plt.subplots(2)
+    ax[0].plot("ones", "twos", data=pts)
+    ax[1].plot("ones", "twos", "r", data=pts)
+
+
 @image_comparison(baseline_images=['const_xy'])
 def test_const_xy():
     fig = plt.figure()
