Calculating the Moving Average of a List

Question

This weekend I decided to try my hand at some Scala and Clojure. I\'m proficient with object oriented programming, and so Scala was easy to pick up as a language, but wante

Answer 1

This example makes use of state, since to me it's a pragmatic solution in this case, and a closure to create the windowing averaging function:

(defn make-averager [#^Integer period]
  (let [buff (atom (vec (repeat period nil)))
        pos (atom 0)]
    (fn [nextval]
      (reset! buff (assoc @buff @pos nextval))
      (reset! pos (mod (+ 1 @pos) period))
      (if (some nil? @buff)
        0
        (/ (reduce + @buff)
           (count @buff))))))

(map (make-averager 4)
     [2.0, 4.0, 7.0, 6.0, 3.0, 8.0, 12.0, 9.0, 4.0, 1.0])
;; yields =>
(0 0 0 4.75 5.0 6.0 7.25 8.0 8.25 6.5)

It is still functional in the sense of making use of first class functions, though it is not side-effect free. The two languages you mentioned both run on top of the JVM and thus both allow for state-management when necessary.