Handled empty values

holoviews/core/data/interface.py

@@ -290,6 +290,8 @@ def range(cls, dataset, dimension):
                 return (np.nanmin(column), np.nanmax(column))
             except TypeError:
                 column = [v for v in util.python2sort(column) if v is not None]
+                if not len(column):
+                    return np.NaN, np.NaN
                 return column[0], column[-1]
 
     @classmethod

holoviews/core/data/pandas.py

@@ -142,6 +142,8 @@ def range(cls, columns, dimension):
             else:
                 column = column.sort_values()
             column = column[~column.isin([None])]
+            if not len(column):
+                return np.NaN, np.NaN
             return column.iloc[0], column.iloc[-1]
         else:
             return (column.min(), column.max())
@@ -292,6 +294,16 @@ def dframe(cls, columns, dimensions):
             return columns.data.copy()
 
 
+    @classmethod
+    def array(cls, dataset, dimensions):
+        if not dimensions:
+            dimensions = dataset.dimensions(label='name')
+        else:
+            dimensions = [dataset.get_dimensions(d).name for d in dimensions]
+        inds = [dataset.data.columns.index(dim.name) for dim in dimensions]
+        return dataset.data.values[:, inds]
+
+
     @classmethod
     def iloc(cls, dataset, index):
         rows, cols = index