List Question

[Shoukat]

Can anyone tell me how to remove an item from a list

Thanks
Shoukat

 

[Marc'Antonio Alessi]

vl-remove Function
Removes elements from a list
(vl-remove element-to-remove list)

Arguments
element-to-remove
The value of the element to be removed; may be any LISP data type.

list
Any list.

Return Values
The list with all elements except those equal to element-to-remove.

Examples

_$ (vl-remove pi (list pi t 0 "abc"))
(T 0 "abc")

or

(vl-remove-if predicate-function list)
Returns all elements of the supplied list that fail the test function

(vl-remove-if-not predicate-function list)
Returns all elements of the supplied list that pass the test function

; for r14 and other needs:

;Tony Tanzillo
(defun remove-at (lst pos / head)
(repeat pos
(setq head (cons (car lst) head)
lst (cdr lst)
)
)
(append (reverse head) (cdr lst))
)

---

; for long list and high nth pos...

(defun remove-at2 (lst pos / head len)
(cond
( (> (/ (setq len (length lst)) 2) pos)
(repeat pos
(setq head (cons (car lst) head)
lst (cdr lst)
)
)
(append (reverse head) (cdr lst))
)
( T
(setq lst (reverse lst))
(repeat (1- (- len pos))
(setq head (cons (car lst) head)
lst (cdr lst)
)
)
(append (reverse (cdr lst)) head)
)
)
)

; index = nth like
; newitm = new item to subst or nil to remove
; lst = original list
; r_lst = original list reversed
;
; Example: (setq rlist (reverse alist))
; (ALE_SUBST_NTH 2 nil alist rlist)

(defun ALE_SUBST_NTH (index newitem lst r_lst / len olditem) (if (> (setq len (- (length lst) (1+ index))) -1) (progn (setq olditem (nth index lst)) (while (/= index (length (setq r_lst (cdr (member olditem r_lst)))))) (while (/= len (length (setq lst (cdr (member olditem lst)))))) (append (reverse r_lst) (if newitem (list newitem) nil) lst) ) lst )
)

;
; removes all the duplicated elements leaving originals, ; faster on lists with low number of duplicates ; example:
; (setq alist2 (atoms-family 1))
; (setq alist2 (append alist2 alist2 alist2 alist2))
;
(defun ALE_RemoveDupOnLst (InLst / OutLst)
(reverse
(foreach ForElm InLst
(if (vl-position ForElm OutLst)
OutLst
(setq OutLst (cons ForElm OutLst))
)
)
)
)
;
; removes all the duplicated elements leaving originals, ; faster on lists with high number of duplicates ; example:
; (setq alst2 nil) (setq alist '(1 2 3 4 4 5 5 5 6 7 8 9 9 9 9)) ; (setq alist2 (repeat 500 (setq alist2 (append alist2 alist)))) ; (defun ALE_RemoveDupOnLst2 (InLst / OutLst CarElm) (while InLst (setq InLst (vl-remove (setq CarElm (car InLst)) (cdr InLst)) OutLst (cons CarElm OutLst) ) ) (reverse OutLst) ) ; ; removes all the duplicated elements leaving originals, ; for R14 ; (defun ALE_RemoveDupOnLst14 (InLst / OutLst) (reverse (foreach ForElm InLst (if (member ForElm OutLst) OutLst (setq OutLst (cons ForElm OutLst)) ) ) )
)

 

[John Uhden]

There are a number of ways, depending on how you want to identify the item to remove:
;;----------------------------------------------------------------- ;; CUT_LIST.LSP (c)1995-96, John F. Uhden, CADvantage ;; This function deletes the first instance of an item from a list:
;; Corrected thanks to trouble shooting by Peter B. Tobey (defun @cv_cut_list (item items / m) (if (setq m (member item items)) (progn (setq items (reverse items)) (repeat (length m)(setq items (cdr items))) (append (reverse items) (cdr m)) ) items ) ) ;;********************************************** ;; NOTE: To cut all, use (vl-remove item items) ;;---------------------------------------------- ;; Tony Tanzillo (01-25-02) (defun @cv_cut_nth (lst pos / head) (repeat pos (setq head (cons (car lst) head) lst (cdr lst) ) ) (append (reverse head) (cdr lst))
)

If the item might have some value that falls within a range or maybe matches a string pattern then you can...
Command: (vl-remove-if '(lambda (x)(wcmatch (strcase x) "*A*"))'("It" "was" "a" "dark" "night"))
("It" "night")

There's also a (vl-remove-if-not) function that works the same way.

 

[Peter Jamtgaard]

What are you trying to do, remove every instance of an item or remove an item based on location like the nth function?

Peter Jamtgaard