Validation, tests for rgb imshow

xarray/plot/plot.py

@@ -453,7 +453,8 @@ def newplotfunc(darray, x=None, y=None, figsize=None, size=None,
             # Convert byte-arrays to float for correct display in matplotlib
             if darray.dtype == np.dtype('uint8'):
                 darray = darray / 256.0
-            # Manually stretch colors for robust cmap
+            # Manually stretch colors for robust cmap.  We have to do this
+            # first so faceted plots are comparable between facets.
             if robust:
                 flat = darray.values.ravel(order='K')
                 flat = flat[~np.isnan(flat)]
@@ -503,6 +504,12 @@ def newplotfunc(darray, x=None, y=None, figsize=None, size=None,
         xlab, ylab = _infer_xy_labels(
             darray=darray, x=x, y=y, imshow=imshow_rgb, rgb=rgb)
 
+        if rgb is not None and plotfunc.__name__ != 'imshow':
+            raise ValueError('The "rgb" keyword is only valid for imshow()')
+        elif rgb is not None and not imshow_rgb:
+            raise ValueError('The "rgb" keyword is only valid for imshow()'
+                             'with a three-dimensional array (per facet)')
+
         # better to pass the ndarrays directly to plotting functions
         xval = darray[xlab].values
         yval = darray[ylab].values

xarray/tests/test_plot.py

@@ -672,6 +672,11 @@ def test_can_plot_axis_size_one(self):
         if self.plotfunc.__name__ not in ('contour', 'contourf'):
             self.plotfunc(DataArray(np.ones((1, 1))))
 
+    def test_disallows_rgb_arg(self):
+        with pytest.raises(ValueError):
+            # Always invalid for most plots.  Invalid for imshow with 2D data.
+            self.plotfunc(DataArray(np.ones((2, 2))), rgb='not None')
+
     def test_viridis_cmap(self):
         cmap_name = self.plotmethod(cmap='viridis').get_cmap().name
         self.assertEqual('viridis', cmap_name)
@@ -1071,6 +1076,13 @@ def test_plot_rgb_image(self):
         ).plot.imshow()
         self.assertEqual(0, len(find_possible_colorbars()))
 
+    def test_plot_rgb_image_explicit(self):
+        DataArray(
+            easy_array((10, 15, 3), start=0),
+            dims=['y', 'x', 'band'],
+        ).plot.imshow(y='y', x='x', rgb='band')
+        self.assertEqual(0, len(find_possible_colorbars()))
+
     def test_plot_rgb_faceted(self):
         DataArray(
             easy_array((2, 2, 10, 15, 3), start=0),
@@ -1093,6 +1105,16 @@ def test_warns_ambigious_dim(self):
         arr.plot.imshow(rgb='band')
         arr.plot.imshow(x='x', y='y')
 
+    def test_rgb_errors_too_many_dims(self):
+        arr = DataArray(easy_array((3, 3, 3, 3)), dims=['y', 'x', 'z', 'band'])
+        with pytest.raises(ValueError):
+            arr.plot.imshow(rgb='band')
+
+    def test_rgb_errors_bad_dim_sizes(self):
+        arr = DataArray(easy_array((5, 5, 5)), dims=['y', 'x', 'band'])
+        with pytest.raises(ValueError):
+            arr.plot.imshow(rgb='band')
+
 
 class TestFacetGrid(PlotTestCase):