Idiomatically refactor Clojure code to improve performance

slide-perf.clj

;; http://johnj.com/from-elegance-to-speed.html

(def times (iterate #(+ % (rand-int 1000)) 0))

(def times-v (into [] (take 1e6) (iterate #(+ % (rand-int 1000)) 0)))

(defn smt-8 [times]
  (->> times
       (partition 8 1)
       (map (juxt identity
                  (comp (partial apply -)
                        (juxt last first))))
       (filter (comp (partial > 1000) second))
       doall))

(cc/quick-bench (smt-8 times-v))

(defn sliding
  ([^long n]
   (sliding n 1))
  ([^long n ^long step]
   (fn [rf]
     (let [a (java.util.ArrayDeque. n)]
       (fn
         ([] (rf))
         ([result]
          (let [result (if (.isEmpty a)
                         result
                         (let [v (vec (.toArray a))]
                           ;;clear first!
                           (.clear a)
                           (unreduced (rf result v))))]
            (rf result)))
         ([result input]
          (.add a input)
          (if (= n (.size a))
            (let [v (clojure.lang.LazilyPersistentVector/createOwning (.toArray a))]
              (dotimes [_ step] (.removeFirst a))
              (rf result v))
            result)))))))

(def smt-xf0
  (comp
   (sliding 8 1)
   (map (juxt identity
              (comp (partial apply -)
                    (juxt last first))))
   (filter (comp (partial > 1000) second))))

(cc/quick-bench (doall (sequence smt-xf0 times-v)))

(def smt-xf1
  (comp
   (sliding 8 1)
   (map (fn [v] [v (- (peek v) (nth v 0))]))
   (filter (fn [v] (> 1000 (nth v 1))))))


(cc/quick-bench (doall (sequence smt-xf1 times-v)))


(def smt-xf2
  (comp
   (sliding 8 1)
   (keep (fn [v] (let [d (- (peek v) (nth v 0))]
                  (when (> 1000 d)
                    [v d]))))))


(cc/quick-bench (doall (sequence smt-xf2 times-v)))

(import 'java.util.ArrayDeque)

(defn sliding*
  ([^long n]
   (sliding* n 1))
  ([^long n ^long step]
   (fn [rf]
     (let [a (ArrayDeque. n)]
       (fn
         ([] (rf))
         ([result]
          (let [result (if (.isEmpty a)
                         result
                         (let [v (.toArray ^ArrayDeque a)]
                           ;;clear first!
                           (.clear a)
                           (unreduced (rf result v))))]
            (rf result)))
         ([result input]
          (.add a input)
          (if (= n (.size a))
            (let [v (.toArray ^ArrayDeque a)]
              (dotimes [_ step] (.removeFirst a))
              (rf result v))
            result)))))))

(def smt-xf3
  (comp
   (sliding* 8 1)
   (keep (fn [^objects arr]
           (let [d (- ^long (aget arr (unchecked-dec-int (alength arr))) ^long (aget arr 0))]
             (when (> 1000 d)
               [arr d]))))))


(do
  (cc/quick-bench (smt-8 times-v)) ;; 1.2 sec
  (cc/quick-bench (doall (sequence smt-xf0 times-v))) ;; 470 ms
  (cc/quick-bench (doall (sequence smt-xf1 times-v))) ;; 54 ms
  (cc/quick-bench (doall (sequence smt-xf2 times-v))) ;; 49 ms
  (cc/quick-bench (doall (sequence smt-xf3 times-v))));; 30 ms