pearson-fast.clj

(defn pearson-fast
  [v1 v2]
  (let [dim (double (count v1))
	meanv1 (/ (areduce v1 i ret 0 
		    (+ ret (aget v1 i))) dim)
	meanv2 (/ (areduce v2 i ret 0 
		    (+ ret (aget v2 i))) dim)
	sum (areduce v1 i ret 0
		    (+ ret (* (- (aget v1 i) meanv1) 
			      (- (aget v2 i) meanv2))))
	norm1 (areduce v1 i ret 0
		    (+ ret (* (Math/pow 
			      (- (aget v1 i) meanv1) 2))))
	norm2 (areduce v1 i ret 0
		    (+ ret (* (Math/pow 
		              (- (aget v2 i) meanv2) 2))))]
    (/ sum (Math/sqrt (* norm1 norm2)))))


user> (def v1 (double-array (take 100 (repeatedly rand))))
user> (def v2 (double-array (take 100 (repeatedly rand))))
user> (dotimes [_ 10] (time (pearson-fast v1 v2)))
"Elapsed time: 0.192087 msecs"
"Elapsed time: 0.261311 msecs"
"Elapsed time: 0.142108 msecs"
"Elapsed time: 0.141602 msecs"
"Elapsed time: 0.145241 msecs"
"Elapsed time: 0.140171 msecs"
"Elapsed time: 0.140597 msecs"
"Elapsed time: 0.140423 msecs"
"Elapsed time: 0.140051 msecs"
"Elapsed time: 0.141224 msecs"

pearson-slow.clj

(defn pearson-slow
  [v1 v2]
  (let [dim (count v1)
	meanv1 (double (/ (reduce + v1) dim))
	meanv2 (double (/ (reduce + v2) dim))
	sum (reduce + (map (fn [i j] 
                             (* (- i meanv1) 
				(- j meanv2))) v1 v2))
	norm1 (reduce + (map (fn [i]
			   (Math/pow (- i meanv1) 2)) v1))
	norm2 (reduce + (map (fn [i]
			   (Math/pow (- i meanv2) 2)) v2))]
    (/ sum (Math/sqrt (* norm1 norm2)))))

user> (def w1 (take 100 (repeatedly rand)))
user> (def w2 (take 100 (repeatedly rand)))
user> (dotimes [_ 10] (time (pearson-slow w1 w2)))
"Elapsed time: 0.570365 msecs"
"Elapsed time: 0.515203 msecs"
"Elapsed time: 0.511854 msecs"
"Elapsed time: 0.509913 msecs"
"Elapsed time: 0.513456 msecs"
"Elapsed time: 0.514767 msecs"
"Elapsed time: 0.519651 msecs"
"Elapsed time: 0.517207 msecs"
"Elapsed time: 0.537696 msecs"
"Elapsed time: 0.521394 msecs"