sequence of a rolling average in Clojure

Question

I'm looking for an elegant way to generate a sequence of the rolling average of a sequence of numbers. Hopefully something more elegant than using lazy-seq

Answer 1

Without any consideration of efficiency:

(defn average [lst] (/ (reduce + lst) (count lst)))

(defn moving-average [window lst] (map average (partition window 1 lst)))


user> (moving-average 5 '(1 2 3 4 5 6 7 8))
(3 4 5 6)

If you need it to be fast, there are some fairly obvious improvements to be made! But it will get less elegant.

Answer 2

There's a very similar question on SO: Calculating the Moving Average of a List. It's more general -- a number of FP-friendly languages are represented, with the accepted answer using Scala -- but there are a few nice Clojure solutions.

I've posted my own solution over there. Note that it does use lazy-seq, but that's because I wanted it to perform well for large periods (which means adjusting the average at each step rather than calculating a separate average for each window of size = period into the input list). Look around that Q for nice solutions which made the other tradeoff, resulting in shorter code with a somewhat more declarative feel, which actually performs better for very short periods (although suffers significant slowdowns for longer periods, as is to be expected).