anti-select elements of a list

[lyl]

The function "select" can be used to select multi-elements of a list at one time, for example:

Code Select Expand

(select '(0 1 2 3 4) '(1 2)) ->(1 2)



Yet what I want is to get all elements other than those "selceted", that is to say, I want to obtain (0 3 4) from above example.

I tried with the function "filter" like this:

Code Select Expand

(filter (not (find $idx '(1 2))) '(0 1 2 3 4))
but it fails because "filter" does not support $idx.



So, is there a better way to anti-select elements in a list at one time by another list which assign positions those elements to be deleted?

[newBert]

Here is a solution (probably not the only one, nor the best) :

Code Select Expand

newLISP v.10.7.5 64-bit on Linux IPv4/6 UTF-8 libffi, options: newlisp -h

> (select '(0 1 2 3 4) (difference (index true? '(0 1 2 3 4)) '(1 2)))
(0 3 4)
> ;; maybe clearer:
>
(let (lst '(0 1 2 3 4))
  (select lst (difference (index true? lst) '(1 2))))

(0 3 4)
>

[lyl]

Here is a solution (probably not the only one, nor the best) :

Code Select Expand

newLISP v.10.7.5 64-bit on Linux IPv4/6 UTF-8 libffi, options: newlisp -h

> (select '(0 1 2 3 4) (difference (index true? '(0 1 2 3 4)) '(1 2)))
(0 3 4)
> ;; maybe clearer:
>
(let (lst '(0 1 2 3 4))
  (select lst (difference (index true? lst) '(1 2))))

(0 3 4)
>

If the lst contains nil(0 1 2 3 nil), how to do?

[fdb]

Code Select Expand


(define (unselect lst sel)
  (clean (fn(x) (member x sel)) lst))

(unselect '( 0 1 2 3 nil) '(1 2))

(0 3 nil)


[fdb]

or just

Code Select Expand


(difference '(0 1 2 3 nil) '(1 2))

(0 3 nil)


or am I misunderstanding something?

[lyl]

@fdb '(1 2) in my example means the position of elements in lst, not elements themselves. I think I give a poor example.

[rrq]

So you might be looking for something like the following:

Code Select Expand

(define (drop lst idx) (let (n -1) (clean (fn (x) (member (inc n) idx)) lst)))

> (drop '(5 4 3 2 1) '(1 2))
(5 2 1)

[newBert]

Here is a solution (probably not the only one, nor the best) :

Code Select Expand

newLISP v.10.7.5 64-bit on Linux IPv4/6 UTF-8 libffi, options: newlisp -h

> (select '(0 1 2 3 4) (difference (index true? '(0 1 2 3 4)) '(1 2)))
(0 3 4)
> ;; maybe clearer:
>
(let (lst '(0 1 2 3 4))
  (select lst (difference (index true? lst) '(1 2))))

(0 3 4)
>

If the lst contains nil(0 1 2 3 nil), how to do?

I replaced 0 1 2 3 4... with a b c d e... for clarity.

Code Select Expand

>
(let (lst '(a b c d nil f))
  (select lst (difference (sequence 0 (- (length lst) 1)) '(1 2))))

(a d nil f)
>

[fdb]

or use select and the difference of the selected indexes:

Code Select Expand


(define (unselect lst sel)
(select lst (difference (sequence 0 (dec (length lst))) sel)))

> (unselect '(5 4 3 2 1) '(1 2))
(5 2 1)


[lyl]

Many thanks all of you for these beautiful solutions!!