Prepare refactoring

comparator.py

@@ -127,14 +127,14 @@ class Comparator(Aggregator, HDF5Container):
         return series
 
     def _comp(self, getter, use_num=True):
-        prop = np.zeros(len(self.runs))
+        prop = []
         for i, run in enumerate(self.runs):
             if use_num:
                 num = self.nums[run][0]
-                prop[i] = getter(run, num)
+                prop.append(getter(run, num))
             else:
-                prop[i] = getter(run)
-        return prop
+                prop.append(getter(run))
+        return np.array(prop)
 
     def _time_avg(self, name, start=None, end=None, span=None, group="/series"):
         mean = np.zeros(len(self.runs))