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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 15:44:07 -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 srfi-1)  ;; list-index
> 
> (define (index x xs) (list-index (cut equal? x <>) xs))
> 
> (define (summarize alist)
>   (let1 keys (delete-duplicates (map car alist) )
>     (map
>       cons
>       keys
>       (apply map
>         +
>         (map
>           (lambda(kv)
>             (let1 v (make-vector (length keys) 0)
>               (vector-set! v (index (car kv) keys) (cadr kv))
>               (vector->list v)))
>           alist)))))
> 
> (summarize '((c 7) (a 1) (a 3) (b 1) (b 10) (b 100)))
>   ===>
> ((c . 7) (a . 4) (b . 111))

Another way:

(define (summarize alist)
  (delete-duplicates
    (fold
      (lambda (kv accum)
        (let* ((k (car kv))
               (v (cdr kv))
               (n (assoc-ref accum k 0)))
          (cons (cons k (+ n v)) accum)))
      '()
      alist)
    (lambda(a b)(equal? (car a)(car b)))))

(summarize '((c . 7) (a . 1) (a . 3) (b . 1) (b . 10) (b . 100)))
  ===>
((b . 111) (a . 4) (c . 7))