Allow lower dimensional views on arbitrary dimensioned elements

holoviews/core/data/grid.py

@@ -329,7 +329,10 @@ def canonicalize(cls, dataset, data, data_coords=None, virtual_coords=[]):
         dropped = [dims.index(d) for d in dims
                    if d not in dataset.kdims+virtual_coords]
         if dropped:
-            data = np.squeeze(data, axis=tuple(dropped))
+            if len(dropped) == data.ndim:
+                data = data.flatten()
+            else:
+                data = np.squeeze(data, axis=tuple(dropped))
 
         if not any(cls.irregular(dataset, d) for d in dataset.kdims):
             inds = [dims.index(kd.name) for kd in dataset.kdims]

holoviews/core/data/xarray.py

@@ -226,7 +226,7 @@ def retrieve_unit_and_label(dim):
                     # Skip if all the dims on the coord are present on another coord
                     continue
                 undeclared.append(c)
-            if undeclared:
+            if undeclared and eltype.param.kdims.bounds[1] not in (0, None):
                 raise DataError(
                     'The coordinates on the %r DataArray do not match the '
                     'provided key dimensions (kdims). The following coords '