10. The computer-implemented method of claim 1 , wherein the online system further maintains feature loops, each feature loop aggregating values of a feature expression across a plurality of actions.
10. The computer-implemented method of claim 1 , wherein the online system further maintains feature loops, each feature loop aggregating values of a feature expression across a plurality of actions. 13. The computer-implemented method of claim 10 , wherein a feature loop aggregates the number of occurrences of an event during a previous time interval.