From 3edd1765d98b59253eb4f7c95af871766918ea9b Mon Sep 17 00:00:00 2001
From: Thomas A Caswell <tcaswell@gmail.com>
Date: Wed, 23 Sep 2020 13:22:26 -0400
Subject: [PATCH] Merge pull request #18549 from
 jklymak/fix-pcolorarg-convert-before-interp

FIX: unit-convert pcolorargs before interpolating
---
 lib/matplotlib/axes/_axes.py      | 21 ++++++++-------------
 lib/matplotlib/tests/test_axes.py | 16 ++++++++++++++++
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 7018bbb3626d..72ca0e6266d4 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -5535,8 +5535,7 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
         self.add_image(im)
         return im
 
-    @staticmethod
-    def _pcolorargs(funcname, *args, shading='flat'):
+    def _pcolorargs(self, funcname, *args, shading='flat', **kwargs):
         # - create X and Y if not present;
         # - reshape X and Y as needed if they are 1-D;
         # - check for proper sizes based on `shading` kwarg;
@@ -5567,6 +5566,10 @@ def _pcolorargs(funcname, *args, shading='flat'):
             # Check x and y for bad data...
             C = np.asanyarray(args[2])
             X, Y = [cbook.safe_masked_invalid(a) for a in args[:2]]
+            # unit conversion allows e.g. datetime objects as axis values
+            self._process_unit_info(xdata=X, ydata=Y, kwargs=kwargs)
+            X = self.convert_xunits(X)
+            Y = self.convert_yunits(Y)
             if funcname == 'pcolormesh':
                 if np.ma.is_masked(X) or np.ma.is_masked(Y):
                     raise ValueError(
@@ -5815,14 +5818,10 @@ def pcolor(self, *args, shading=None, alpha=None, norm=None, cmap=None,
         if shading is None:
             shading = rcParams['pcolor.shading']
         shading = shading.lower()
-        X, Y, C, shading = self._pcolorargs('pcolor', *args, shading=shading)
+        X, Y, C, shading = self._pcolorargs('pcolor', *args, shading=shading,
+                                            kwargs=kwargs)
         Ny, Nx = X.shape
 
-        # unit conversion allows e.g. datetime objects as axis values
-        self._process_unit_info(xdata=X, ydata=Y, kwargs=kwargs)
-        X = self.convert_xunits(X)
-        Y = self.convert_yunits(Y)
-
         # convert to MA, if necessary.
         C = ma.asarray(C)
         X = ma.asarray(X)
@@ -6091,14 +6090,10 @@ def pcolormesh(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
         kwargs.setdefault('edgecolors', 'None')
 
         X, Y, C, shading = self._pcolorargs('pcolormesh', *args,
-                                            shading=shading)
+                                            shading=shading, kwargs=kwargs)
         Ny, Nx = X.shape
         X = X.ravel()
         Y = Y.ravel()
-        # unit conversion allows e.g. datetime objects as axis values
-        self._process_unit_info(xdata=X, ydata=Y, kwargs=kwargs)
-        X = self.convert_xunits(X)
-        Y = self.convert_yunits(Y)
 
         # convert to one dimensional arrays
         C = C.ravel()
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index 41df0f502347..c0d2181ace62 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -1188,6 +1188,22 @@ def test_pcolornearest(fig_test, fig_ref):
     ax.pcolormesh(x2, y2, Z, shading='nearest')
 
 
+@check_figures_equal(extensions=["png"])
+def test_pcolornearestunits(fig_test, fig_ref):
+    ax = fig_test.subplots()
+    x = [datetime.datetime.fromtimestamp(x * 3600) for x in range(10)]
+    y = np.arange(0, 3)
+    np.random.seed(19680801)
+    Z = np.random.randn(2, 9)
+    ax.pcolormesh(x, y, Z, shading='flat')
+
+    ax = fig_ref.subplots()
+    # specify the centers
+    x2 = [datetime.datetime.fromtimestamp((x + 0.5) * 3600) for x in range(9)]
+    y2 = y[:-1] + np.diff(y) / 2
+    ax.pcolormesh(x2, y2, Z, shading='nearest')
+
+
 @check_figures_equal(extensions=["png"])
 def test_pcolordropdata(fig_test, fig_ref):
     ax = fig_test.subplots()