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

A short Clojure version that has the advantage of being O(list length) regardless of your period:

(defn moving-average [list period]
  (let [accums (let [acc (atom 0)] (map #(do (reset! acc (+ @acc %1 ))) (cons 0 list)))
        zeros (repeat (dec period) 0)]
     (concat zeros (map #(/ (- %1 %2) period) (drop period accums) accums))))

This exploits the fact that you can calculate the sum of a range of numbers by creating a cumulative sum of the sequence (e.g. [1 2 3 4 5] -> [0 1 3 6 10 15]) and then subtracting the two numbers with an offset equal to your period.