Wade Humeniuk wrote:

> Yeah, but I do not worry about it, much, at the beginning. Here
> is another, it seems easier to think in the morning
>
> (defun summarize (list)
> (let ((summary nil))
> (map nil (lambda (elt)
> (let ((sum (find (first elt) summary :test #'eql :key #'first)))
> (if sum
> (incf (second sum) (second elt))
> (push elt summary))))
> list)
> summary))
>
> and its loop version
>
> (defun summarize (list)
> (loop with summary = nil
> for elt in list
> for sum = (find (first elt) summary :test #'eql :key #'first)
> if sum do (incf (second sum) (second elt))
> else do (push elt summary)
> finally (return summary)))
>
> CL-USER 2 > (summarize '((c 7) (a 1) (a 3) (b 1) (b 10) (b 100)))
> ((B 111) (A 4) (C 7))

Gauche Scheme:

(use srfi-1) ;; unzip2

(define (summarize alist)
(define (kons k v a)
(cons
(cons k (+ v (assoc-ref a k 0)))
(alist-delete k a)))
(apply fold
kons
'()
(values->list (unzip2 alist))))

(summarize '((c 7) (a 1) (a 3) (b 1) (b 10) (b 100)))

===>
((b . 111) (a . 4) (c . 7))