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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 02:19:34 -0000 (UTC)
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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))