Re: Exercises, chap. 3, Graham

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))]))