Re: Remove the occurences of a given element from a list.

Pascal Bourguignon wrote:

Here is for example, a function that is both iterative and
recursive. but not stupid (even if it could be written better with
LOOP):
 
(defun find-depths (target list)
  "Returns a list of depths where occurences of TARGET are found in LIST"
  (let ((results '()))
    (dolist (item list (nreverse (mapcar (function 1+) results)))
      (cond
       ((eql target item)
        (push 0 results))
       ((listp item)
        (setf results (nreconc (find-depths target item) results)))))))
 
C/USER[139]> (find-depths 'a '(a a ((a b (c a d))) a))
(1 1 3 4 1)
C/USER[140]> (find-depths 'a '(a (((a)))))
(1 4)

Gauche Scheme

(define (find-depths target lst :optional (depth 1))
  (append-map
    (lambda (item)
      (cond ((eqv? item target) (list depth))
            ((list? item) (find-depths target item (+ depth 1)))
            (#t '())))
    lst))

(find-depths 'a '(a a ((a b (c a d))) a))
  ===>
(1 1 3 4 1)

(find-depths 'a '(a (((a)))))
  ===>
(1 4)