anti-select elements of a list

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lyl
Posts: 39
Joined: Sun Mar 25, 2018 5:00 am

anti-select elements of a list

Post by lyl »

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

Code: Select all

(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 all

(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
Posts: 145
Joined: Fri Oct 28, 2005 5:33 pm
Location: France

Re: anti-select elements of a list

Post by newBert »

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

Code: Select all

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)
>
BertrandnewLISP v.10.7.6 64-bit on Linux (Peppermint 9)

lyl
Posts: 39
Joined: Sun Mar 25, 2018 5:00 am

Re: anti-select elements of a list

Post by lyl »

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

Code: Select all

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
Posts: 57
Joined: Sat Nov 09, 2013 8:49 pm

Re: anti-select elements of a list

Post by fdb »

Code: Select all

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

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

(0 3 nil)

fdb
Posts: 57
Joined: Sat Nov 09, 2013 8:49 pm

Re: anti-select elements of a list

Post by fdb »

or just

Code: Select all

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

(0 3 nil)
or am I misunderstanding something?

lyl
Posts: 39
Joined: Sun Mar 25, 2018 5:00 am

Re: anti-select elements of a list

Post by lyl »

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

ralph.ronnquist
Posts: 216
Joined: Mon Jun 02, 2014 1:40 am
Location: Melbourne, Australia

Re: anti-select elements of a list

Post by ralph.ronnquist »

So you might be looking for something like the following:

Code: Select all

(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
Posts: 145
Joined: Fri Oct 28, 2005 5:33 pm
Location: France

Re: anti-select elements of a list

Post by newBert »

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

Code: Select all

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 all

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

(a d nil f)
>
Last edited by newBert on Sat Dec 22, 2018 12:42 pm, edited 1 time in total.
BertrandnewLISP v.10.7.6 64-bit on Linux (Peppermint 9)

fdb
Posts: 57
Joined: Sat Nov 09, 2013 8:49 pm

Re: anti-select elements of a list

Post by fdb »

or use select and the difference of the selected indexes:

Code: Select all

(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
Posts: 39
Joined: Sun Mar 25, 2018 5:00 am

Re: anti-select elements of a list

Post by lyl »

Many thanks all of you for these beautiful solutions!!

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