Quick attempt at sum-for-x-events in Riemann

gistfile1.clj

(defn sum-for-count
  "Emit the sum of the last n events."
  [n & children]
  (let [window (ref (vec (repeat n 0)))]
    (fn [event]
      ; here we guard against putting nils in our vector which doesn't work with (reduce + ... )
      (if (and (contains? event :metric)
               (not (nil? (:metric event))))
        (do
          (dosync (alter window pop)
                  (ref-set window (into [(:metric event)] @window)))
          (call-rescue
            (assoc event :description (str "Sum of last " n " events.") :metric (reduce + @window) :service (str (:service event) " sum"))
              children))))))