Fixed bug aggregating empty BoxWhisker/Violin (#3397)

holoviews/plotting/bokeh/stats.py

@@ -8,7 +8,7 @@
 
 from bokeh.models import FactorRange, Circle, VBar, HBar
 
-from ...core.dimension import Dimension
+from ...core.dimension import Dimension, Dimensioned
 from ...core.ndmapping import sorted_context
 from ...core.util import (basestring, dimension_sanitizer, wrap_tuple,
                           unique_iterator, isfinite)
@@ -102,7 +102,11 @@ def _apply_transforms(self, element, data, ranges, style, group=None):
         if element.ndims > 0:
             element = element.aggregate(function=np.mean)
         else:
-            element = element.clone([(element.aggregate(function=np.mean),)])
+            agg = element.aggregate(function=np.mean)
+            if isinstance(agg, Dimensioned):
+                element = agg
+            else:
+                element = element.clone([(element,)])
         return super(BoxWhiskerPlot, self)._apply_transforms(element, data, ranges, style, group)
 
     def _get_factors(self, element):
@@ -345,8 +349,11 @@ def _kde_data(self, el, key, **kwargs):
         elif self.inner == 'quartiles':
             for stat_fn in self._stat_fns:
                 stat = stat_fn(values)
-                sidx = np.argmin(np.abs(xs-stat))
-                sx, sy = xs[sidx], ys[sidx]
+                if len(xs):
+                    sidx = np.argmin(np.abs(xs-stat))
+                    sx, sy = xs[sidx], ys[sidx]
+                else:
+                    continue
                 segments['x'].append(sx)
                 segments['y0'].append(key+(-sy[-1],))
                 segments['y1'].append(sy)