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From: "B. Pym" <No_spamming@noWhere_7073.org>
Newsgroups: comp.lang.lisp
Subject: Re: How to improve my summarizing code
Date: Mon, 24 Jun 2024 18:04:16 -0000 (UTC)
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On 6/23/2024, B. Pym wrote:

> 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 gauche.sequence)  ;; group-sequence
> 
> (define (summarize alist)
>   (map
>     (lambda(xs) (list (caar xs) (fold + 0 (map cadr xs)))) 
>     (group-sequence alist :key car)))
> 
> (summarize '((c 7) (a 1) (a 3) (b 1) (b 10) (b 100)))
>   ===>
> ((c 7) (a 4) (b 111))

Another way:

(use util.match)

(define (summarize assoclist)
  (define tree (make-tree-map))
  (for-each 
    (match-lambda
      [(key val) (tree-map-update! tree key (cut + <> val) 0)])
    assoclist)
  (tree-map->alist tree))

(summarize '((c 7) (a 1) (a 3) (b 1) (b 10) (b 100)))
  ===>
((a . 4) (b . 111) (c . 7))