Insert Nth
Function Syntax | (LM:insertnth <x> <n> <l>) |
Current Version | 1.0 |
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Arguments | ||
---|---|---|
Symbol | Type | Description |
x | List or Atom | Item to be inserted |
n | Integer | Zero-based index at which to insert item |
l | List | List in which item is to be inserted |
Returns | ||
Type | Description | |
List | List with item inserted at nth position |
Function Description
This function will insert an item ('x') at the n^{th} position in a list ('l').
The index n is zero-based (that is, the first position in the list has index 0) in line with standard AutoLISP functions and most other programming conventions. If the supplied index is less than zero or greater than or equal to the number of items in the list, the supplied list will be returned without modification.
Recursive Version
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;; Insert Nth - Lee Mac ;; Inserts an item at the nth position in a list. ;; x - [any] Item to be inserted ;; n - [int] Zero-based index at which to insert item ;; l - [lst] List in which item is to be inserted (defun LM:insertnth ( x n l ) (cond ( (null l) nil) ( (< 0 n) (cons (car l) (LM:insertnth x (1- n) (cdr l)))) ( (cons x l)) ) )
Iterative Version
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;; Insert Nth - Lee Mac ;; Inserts an item at the nth position in a list. ;; x - [any] Item to be inserted ;; n - [int] Zero-based index at which to insert item ;; l - [lst] List in which item is to be inserted (defun LM:insertnth ( x n l / i ) (setq i -1) (apply 'append (mapcar '(lambda ( a ) (if (= n (setq i (1+ i))) (list x a) (list a))) l)) )
Example Function Calls
_$ (LM:insertnth "A" 3 '(0 1 2 3 4 5)) (0 1 2 "A" 3 4 5)
_$ (LM:insertnth 1 4 '("A" "B" "C" "D" "E")) ("A" "B" "C" "D" 1 "E")