Merge pull request #12124 from dstansby/empty-units

tacaswell · web-flow · commit d0e408e42d2d · 2018-09-15T22:57:01.000-04:00
FIX: Correctly infer units from empty arrays
diff --git a/lib/matplotlib/tests/test_units.py b/lib/matplotlib/tests/test_units.py
@@ -127,3 +127,8 @@ def test_jpl_barh_units():
     fig, ax = plt.subplots()
     ax.barh(x, w, left=b)
     ax.set_xlim([b-1*day, b+w[-1]+1*day])
+
+
+def test_emtpy_arrays():
+    # Check that plotting an empty array with a dtype works
+    plt.scatter(np.array([], dtype='datetime64[ns]'), np.array([]))
diff --git a/lib/matplotlib/units.py b/lib/matplotlib/units.py
@@ -160,13 +160,16 @@ def get_converter(self, x):
             x = x.values
 
         # If x is an array, look inside the array for data with units
-        if isinstance(x, np.ndarray) and x.size:
+        if isinstance(x, np.ndarray):
+            # If there are no elements in x, infer the units from its dtype
+            if not x.size:
+                return self.get_converter(np.array([0], dtype=x.dtype))
             xravel = x.ravel()
             try:
                 # pass the first value of x that is not masked back to
                 # get_converter
                 if not np.all(xravel.mask):
-                    # some elements are not masked
+                    # Get first non-masked item
                     converter = self.get_converter(
                         xravel[np.argmin(xravel.mask)])
                     return converter
