List Question

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

Thanks
Shoukat

 

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))
)
)
)
)



--
________________________________________________

Marc'Antonio Alessi (TV) Italy
(strcat "NOT a " (substr (ver) 8 4) " guru.")

O.S. = XP Pro 2002 - Sp.1 - Ita
AutoCAD = 2004 Ita - Sp.1
________________________________________________

 

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.

 

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