Allow using masked array as offsets

Author: chahak13

lib/matplotlib/collections.py

@@ -545,9 +545,9 @@ def set_offsets(self, offsets):
         offsets = np.asanyarray(offsets)
         if offsets.shape == (2,):  # Broadcast (2,) -> (1, 2) but nothing else.
             offsets = offsets[None, :]
-        self._offsets = np.column_stack(
-            (np.asarray(self.convert_xunits(offsets[:, 0]), float),
-             np.asarray(self.convert_yunits(offsets[:, 1]), float)))
+        self._offsets = np.ma.column_stack(
+            (np.asanyarray(self.convert_xunits(offsets[:, 0]), float),
+             np.asanyarray(self.convert_yunits(offsets[:, 1]), float)))
         self.stale = True
 
     def get_offsets(self):

lib/matplotlib/tests/test_collections.py

@@ -1149,3 +1149,14 @@ def test_check_masked_offsets():
 
     fig, ax = plt.subplots()
     ax.scatter(unmasked_x, masked_y)
+
+
+def test_masked_set_offsets():
+    x = np.ma.array([1, 2, 3, 4, 5], mask=[0, 0, 1, 1, 0])
+    y = np.arange(1, 6)
+
+    fig, ax = plt.subplots()
+    scat = ax.scatter(x, y)
+    x += 1
+    scat.set_offsets(np.ma.column_stack([x, y]))
+    assert np.ma.is_masked(scat.get_offsets())