Support cticks (#1368)

Co-authored-by: maximlt <mliquet@anaconda.com>

doc/reference/xarray/image.ipynb

@@ -79,6 +79,22 @@
     "data.hvplot.image(x='lon', y='lat', z='air', title=time, clabel='T [C]')"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We can also override the colorbar ticks and labels with `cticks`, specified as an integer, list of ticks positions, or list of tuples of the tick positions and labels."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "data.hvplot.image(x='lon', y='lat', z='air', title=time, clabel='T [C]', cticks=[(-40, \"Below Freezing\"), (0, \"Freezing\"), (40, \"Above Freezing\")])"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},

doc/user_guide/Customization.ipynb

@@ -122,8 +122,8 @@
     "        Axis labels for the x-axis, y-axis, and colorbar\n",
     "    xlim/ylim (default=None): tuple or list\n",
     "        Plot limits of the x- and y-axis\n",
-    "    xticks/yticks (default=None): int or list\n",
-    "        Ticks along x- and y-axis specified as an integer, list of\n",
+    "    xticks/yticks/cticks (default=None): int or list\n",
+    "        Ticks along x-axis, y-axis, and colorbar specified as an integer, list of\n",
     "        ticks positions, or list of tuples of the tick positions and labels\n",
     "    width (default=700)/height (default=300): int\n",
     "        The width and height of the plot in pixels\n",

hvplot/converter.py

@@ -207,8 +207,8 @@ class HoloViewsConverter:
         Axis labels for the x-axis, y-axis, and colorbar
     xlim/ylim (default=None): tuple or list
         Plot limits of the x- and y-axis
-    xticks/yticks (default=None): int or list
-        Ticks along x- and y-axis specified as an integer, list of
+    xticks/yticks/cticks (default=None): int or list
+        Ticks along x-axis, y-axis, and colorbar specified as an integer, list of
         ticks positions, or list of tuples of the tick positions and labels
     width (default=700)/height (default=300): int
         The width and height of the plot in pixels
@@ -402,6 +402,7 @@ class HoloViewsConverter:
         'colormap',
         'fontsize',
         'c',
+        'cticks',
         'cmap',
         'color_key',
         'cnorm',
@@ -550,6 +551,7 @@ def __init__(
         invert=False,
         stacked=False,
         colorbar=None,
+        cticks=None,
         datashade=False,
         rasterize=False,
         downsample=None,
@@ -784,6 +786,12 @@ def __init__(
             plot_opts['colorbar'] = True
         elif self.rasterize:
             plot_opts['colorbar'] = plot_opts.get('colorbar', True)
+        if plot_opts.get('colorbar') is True and cticks is not None:
+            if self._backend == 'plotly':
+                raise ValueError('cticks option is not supported for plotly backend')
+            key = 'cticks' if self._backend == 'bokeh' else 'cbar_ticks'
+            self._style_opts[key] = cticks
+
         if 'logz' in kwds and 'logz' in self._kind_options.get(self.kind, {}):
             plot_opts['logz'] = kwds.pop('logz')
         if invert:

hvplot/tests/testoptions.py

@@ -592,3 +592,11 @@ def test_dataset_scatter_with_title(self, ds2, backend):
         plot = ds_sel.hvplot.scatter(x='foo', y='bar')  # Image plot
         opts = Store.lookup_options(backend, plot, 'plot')
         assert opts.kwargs['title'] == 'time = 0, y = 0, x = 0, band = 0'
+
+
+@pytest.mark.usefixtures('load_xarray_accessor')
+class TestXarrayCticks:
+    def test_cticks(self, da2):
+        plot = da2.isel(other=0).hvplot(cticks=[5, 10])
+        handles = hv.renderer('bokeh').get_plot(plot).handles
+        assert handles['colorbar'].ticker.ticks == [5, 10]