Merge pull request matplotlib#15347 from alexrudy/hist-datetime-bins

Fix axes.hist bins units

Author: dstansby

lib/matplotlib/axes/_axes.py

@@ -6573,6 +6573,9 @@ def hist(self, x, bins=None, range=None, density=False, weights=None,
         if bin_range is not None:
             bin_range = self.convert_xunits(bin_range)
 
+        if not cbook.is_scalar_or_string(bins):
+            bins = self.convert_xunits(bins)
+
         # We need to do to 'weights' what was done to 'x'
         if weights is not None:
             w = cbook._reshape_2D(weights, 'weights')

lib/matplotlib/tests/test_axes.py

@@ -1753,6 +1753,29 @@ def test_hist_datetime_datasets():
     ax.hist(data, stacked=False)
 
 
+@pytest.mark.parametrize("bins_preprocess",
+                         [mpl.dates.date2num,
+                          lambda bins: bins,
+                          lambda bins: np.asarray(bins).astype('datetime64')],
+                         ids=['date2num', 'datetime.datetime',
+                              'np.datetime64'])
+def test_hist_datetime_datasets_bins(bins_preprocess):
+    data = [[datetime.datetime(2019, 1, 5), datetime.datetime(2019, 1, 11),
+             datetime.datetime(2019, 2, 1), datetime.datetime(2019, 3, 1)],
+            [datetime.datetime(2019, 1, 11), datetime.datetime(2019, 2, 5),
+             datetime.datetime(2019, 2, 18), datetime.datetime(2019, 3, 1)]]
+
+    date_edges = [datetime.datetime(2019, 1, 1), datetime.datetime(2019, 2, 1),
+                  datetime.datetime(2019, 3, 1)]
+
+    fig, ax = plt.subplots()
+    _, bins, _ = ax.hist(data, bins=bins_preprocess(date_edges), stacked=True)
+    np.testing.assert_allclose(bins, mpl.dates.date2num(date_edges))
+
+    _, bins, _ = ax.hist(data, bins=bins_preprocess(date_edges), stacked=False)
+    np.testing.assert_allclose(bins, mpl.dates.date2num(date_edges))
+
+
 @pytest.mark.parametrize('data, expected_number_of_hists',
                          [([], 1),
                           ([[]], 1),