Performance Problem with Clojure Array

Question

This piece of code is very slow. Execution from the slime-repl on my netbook takes a couple minutes.

(def test-array (make-array Integer/TYPE 400 400 3))

(doseq [x (range 400), y (range 400), z (range 3)]
   (aset test-array x y z 0))

Conversely, this code runs really fast:

(def max-one (apply max (map (fn [w] (apply max (map #(first %) w))) test-array)))
(def max-two (apply max (map (fn [w] (apply max (map #(second %) w))) test-array)))
(def max-three (apply max (map (fn [w] (apply max (map #(last %) w))) test-array)))

Does this have something to do with chunked sequences? Is my first example just written wrong?

Answer 1

You're hitting Java reflection. This blog post has a workaround:

http://clj-me.cgrand.net/2009/10/15/multidim-arrays/