Support masked dates

oscargus · oscargus · commit b7a70c858da8 · 2022-12-15T16:06:16.000+01:00
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
@@ -444,7 +444,9 @@ def date2num(d):
     if not iterable:
         d = [d]
 
-    d = np.asarray(d)
+    masked = np.any(np.ma.getmask(d))
+    d = np.ma.asarray(d) if masked else np.asarray(d)
+
     # convert to datetime64 arrays, if not already:
     if not np.issubdtype(d.dtype, np.datetime64):
         # datetime arrays
@@ -455,7 +457,7 @@ def date2num(d):
         if tzi is not None:
             # make datetime naive:
             d = [dt.astimezone(UTC).replace(tzinfo=None) for dt in d]
-            d = np.asarray(d)
+            d = np.ma.asarray(d) if masked else np.asarray(d)
         d = d.astype('datetime64[us]')
 
     d = _dt64_to_ordinalf(d)
diff --git a/lib/matplotlib/tests/test_dates.py b/lib/matplotlib/tests/test_dates.py
@@ -69,6 +69,18 @@ def test_date2num_NaT_scalar(units):
     assert np.isnan(tmpl)
 
 
+def test_date2num_masked():
+    base = datetime.datetime(2005, 2, 1)
+    dates = np.ma.array([base + datetime.timedelta(days=(2 * i))
+                         for i in range(7)], mask=[0, 1, 1, 0, 0, 0, 1])
+    refmask = np.ma.getmask(dates)
+    npdates = mdates.date2num(dates)
+    np.testing.assert_array_equal(refmask, np.ma.getmask(npdates))
+    np.testing.assert_array_equal(np.ma.getmask(npdates),
+                                  (False, True, True, False, False, False,
+                                   True))
+
+
 def test_date_empty():
     # make sure we do the right thing when told to plot dates even
     # if no date data has been presented, cf
