[aggregator] get all postprocessors, map function

aggregator.py

@@ -19,6 +19,12 @@ def _map_rule(rule, arg, overwrite, path, path_out, pp_params, run_num):
 
 
 class Aggregator:
+    def get_pp_list(self):
+        return [self.pp[run][num] for run in self.runs for num in self.nums[run]]
+
+    def map(self, func):
+        return [func(pp) for pp in self.get_pp_list()]
+
     def _not_self_dep(self, name, dep, dep_arg, overwrite, select):
         if select is not None:
             runs, nums = self.selector.select(**select)