From Newsgroup: comp.lang.lisp

Alan Crowe wrote:

(defun occurrences-CL-condensed (list)
(sort (loop for x in (remove-duplicates list)
collect (cons x (count x list)))
#'> :key #'cdr))

Gauche Scheme

(define (occurrences-GS-condensed List)
(sort
(map
(^x (cons x (count (pa$ equal? x) List)))
(delete-duplicates List))
> cdr))

Testing.

(occurrences-GS-condensed '(a b c d e f b c d e b c d))

===>
((b . 3) (c . 3) (d . 3) (e . 2) (a . 1) (f . 1))


Shorter yet.

(define (occurrences-GS-condensed List)
(sort
(map
(^x (cons x (count (is x) List)))
(delete-duplicates List))
> cdr))

Given:

(define is
(case-lambda
[(x) (lambda(y) (equal? y x))]
[(pred x) (lambda(y) (pred y x))]
[(pred key x) (lambda(y) (pred (key y) x))]))
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