Drop z dimension from ImageStack DataArray before shading

holoviews/core/data/xarray.py

@@ -93,7 +93,7 @@ def retrieve_unit_and_label(dim):
         if isinstance(data, xr.DataArray):
             kdim_len = len(kdim_param.default) if kdims is None else len(kdims)
             vdim_len = len(vdim_param.default) if vdims is None else len(vdims)
-            if vdim_len > 1 and kdim_len == len(data.dims)-1 and data.shape[-1] == vdim_len:
+            if kdim_len == len(data.dims)-1 and data.shape[-1] == vdim_len:
                 packed = True
             elif vdims:
                 vdim = vdims[0]
@@ -446,7 +446,11 @@ def unpack_scalar(cls, dataset, data):
         Given a dataset object and data in the appropriate format for
         the interface, return a simple scalar.
         """
-        if not cls.packed(dataset) and len(data.data_vars) == 1:
+        if cls.packed(dataset):
+            array = data.squeeze()
+            if len(array.shape) == 0:
+                return array.item()
+        elif len(data.data_vars) == 1:
             array = data[dataset.vdims[0].name].squeeze()
             if len(array.shape) == 0:
                 return array.item()

holoviews/operation/datashader.py

@@ -1289,10 +1289,23 @@ def _process(self, element, key=None):
         kdims = element.kdims
         if isinstance(element, ImageStack):
             vdim = element.vdims
+            if element.interface.datatype != 'xarray':
+                element = element.clone(datatype=['xarray'])
             array = element.data
-            if hasattr(array, "to_array"):
-                array = array.to_array("z")
-            array = array.transpose(*[kdim.name for kdim in kdims], ...)
+            # If data is a Dataset it has to be converted to a
+            # DataArray, either by selecting the singular value
+            # dimension or by adding a z-dimension
+            kdims = [kdim.name for kdim in kdims]
+            if not element.interface.packed(element):
+                if len(vdim) == 1:
+                    array = array[vdim[0].name]
+                else:
+                    array = array.to_array("z")
+                    # If data is 3D then we have one extra constant dimension
+                    if array.ndim > 3:
+                        drop = [d for d in array.dims if d not in kdims+["z"]]
+                        array = array.squeeze(drop)
+            array = array.transpose(*kdims, ...)
         else:
             vdim = element.vdims[0].name
             array = element.data[vdim]
@@ -1335,7 +1348,7 @@ def _process(self, element, key=None):
         if self.p.clims:
             shade_opts['span'] = self.p.clims
         elif ds_version > Version('0.5.0') and self.p.cnorm != 'eq_hist':
-            shade_opts['span'] = element.range(vdim)
+            shade_opts['span'] = (array.min(), array.max())
 
         params = dict(get_param_values(element), kdims=kdims,
                       bounds=bounds, vdims=RGB.vdims[:],