From a689f095f6f643649361f3eda0eb2728dd441ed6 Mon Sep 17 00:00:00 2001
From: Ryan May <rmay31@gmail.com>
Date: Thu, 1 Mar 2018 15:48:44 -0700
Subject: [PATCH] Backport PR #10631: Convert NaT to nan in date2num

---
 lib/matplotlib/dates.py            |  7 +++++++
 lib/matplotlib/tests/test_dates.py | 21 ++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
index 3e5baa1c1c03..3c9a67e04a92 100644
--- a/lib/matplotlib/dates.py
+++ b/lib/matplotlib/dates.py
@@ -290,6 +290,13 @@ def _dt64_to_ordinalf(d):
     dt += extra.astype(np.float64) / 1.0e9
     dt = dt / SEC_PER_DAY + 1.0
 
+    NaT_int = np.datetime64('NaT').astype(np.int64)
+    d_int = d.astype(np.int64)
+    try:
+        dt[d_int == NaT_int] = np.nan
+    except TypeError:
+        if d_int == NaT_int:
+            dt = np.nan
     return dt
 
 
diff --git a/lib/matplotlib/tests/test_dates.py b/lib/matplotlib/tests/test_dates.py
index fbdf054b1882..dfc5d3bda399 100644
--- a/lib/matplotlib/tests/test_dates.py
+++ b/lib/matplotlib/tests/test_dates.py
@@ -51,7 +51,8 @@ def test_date_numpyx():
                                   datetime.datetime(2017, 1, 1, 3, 1, 1)]]])
 @pytest.mark.parametrize('dtype', ['datetime64[s]',
                                     'datetime64[us]',
-                                    'datetime64[ms]'])
+                                    'datetime64[ms]',
+                                    'datetime64[ns]'])
 def test_date_date2num_numpy(t0, dtype):
     time = mdates.date2num(t0)
     tnp = np.array(t0, dtype=dtype)
@@ -59,6 +60,24 @@ def test_date_date2num_numpy(t0, dtype):
     assert np.array_equal(time, nptime)
 
 
+@pytest.mark.parametrize('dtype', ['datetime64[s]',
+                                    'datetime64[us]',
+                                    'datetime64[ms]',
+                                    'datetime64[ns]'])
+def test_date2num_NaT(dtype):
+    t0 = datetime.datetime(2017, 1, 1, 0, 1, 1)
+    tmpl = [mdates.date2num(t0), np.nan]
+    tnp = np.array([t0, 'NaT'], dtype=dtype)
+    nptime = mdates.date2num(tnp)
+    np.testing.assert_array_equal(tmpl, nptime)
+
+
+@pytest.mark.parametrize('units', ['s', 'ms', 'us', 'ns'])
+def test_date2num_NaT_scalar(units):
+    tmpl = mdates.date2num(np.datetime64('NaT', units))
+    assert np.isnan(tmpl)
+
+
 @image_comparison(baseline_images=['date_empty'], extensions=['png'])
 def test_date_empty():
     # make sure mpl does the right thing when told to plot dates even