Pascal Costanza wrote:

> > I don't need a general purpose transformation, just some guidelines to
> > follow when I see code like this.
>
> General guideline: Look for a solution that uses LOOP. ;)
>
> (defun diff3 (list)
> (let ((avg (loop for element in list
> sum element into sum
> count t into length
> finally (return (/ sum length)))))
> (loop for element in list
> collect (- element avg))))

Gauche Scheme

(define (diff3 lst :optional (seen '()) (sum 0) (cnt 0))
(if (null? lst)
(let1 avg (/ sum cnt)
(map (cut - <> avg) (reverse seen)))
(let1 x (car lst)
(diff3 (cdr lst) (cons x seen) (+ sum x) (+ cnt 1)))))

(diff3 '(1 2 3 4 5))
===>
(-2 -1 0 1 2)