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Re: Subject: Re: Detele repeated in a list

Cross-posted to 2 groups.

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B. Pym wrote:

> Mariano Montone wrote:
> 
> > > I have this piece of code, that sould delete all the repeated elements
> > > from a list :
> > > 
> > > (defun apaga-repetidos (lista)
> > >  (let ((p (first lista))
> > >     (r (rest lista)))
> > >   (if (null lista)
> > >     nil
> > >   (if (equal p r)
> > >     (apaga-repetidos r)
> > >     (cons p (apaga-repetidos r))))))
> > > 
> > 
> > You are comparing an element with a list when you do (equal p r)
> > 
> > Try this:
> > 
> > (defun apaga-repetidos (lista)
> >    (apaga-repetidos-2 lista (make-hash-table :test #'equal)))
> > 
> > (defun apaga-repetidos-2 (lista vistos)
> >    (if (null lista)
> >        nil
> >        (let ((p (first lista))
> >              (r (rest lista)))
> >          (if (gethash p vistos)
> >              (apaga-repetidos-2 r vistos)
> >              (progn
> >                (setf (gethash p vistos) t)
> >                (cons p (apaga-repetidos-2 r vistos)))))))
> > 
> > > > : (apaga-repetidos '((1 2) (2 2) (3 2) (4 2) (5 2)
> >   (6 2) (7 2) (8 2) (8 3) (8 4) (7 4) (6 4) (5 4) (4 4)
> >   (4 5) (3 5) (3 6) (4 6) (4 5) (4 4) (5 4) ))
> > 
> > Result: ((1 2) (2 2) (3 2) (4 2) (5 2) (6 2) (7 2) (8 2) (8 3) (8 4)
> > (7 4) (6 4) (5 4)
> >  (4 4) (4 5) (3 5) (3 6) (4 6))
> 
> 
> (define (rem-dups List)
>   (do ((res '() (if (member x res) res (cons x res)))
>        (x #f))
>     ((null? List)  res)
>     (set! x (pop! List))))
> 
> 
> (rem-dups '((1 2) (2 2) (3 2) (4 2) (5 2)
>   (6 2) (7 2) (8 2) (8 3) (8 4) (7 4) (6 4) (5 4) (4 4)
>   (4 5) (3 5) (3 6) (4 6) (4 5) (4 4) (5 4)))
>   ===>
> ((4 6) (3 6) (3 5) (4 5) (4 4) (5 4) (6 4) (7 4) (8 4) (8 3) (8 2)
>  (7 2) (6 2) (5 2) (4 2) (3 2) (2 2) (1 2))

Shorter:

(define (rem-dups List)
  (Do ((r '() (if (member x r) r (cons x r)))
       (x (pop List) <>))
    ((null? List) @ r)))

(rem-dups '((1 2) (2 2) (3 2) (4 2) (5 2)
  (6 2) (7 2) (8 2) (8 3) (8 4) (7 4) (6 4) (5 4) (4 4)
  (4 5) (3 5) (3 6) (4 6) (4 5) (4 4) (5 4)))
  ===>
((1 2) (2 2) (3 2) (4 2) (5 2) (6 2) (7 2) (8 2) (8 3) (8 4)
 (7 4) (6 4) (5 4) (4 4) (4 5) (3 5) (3 6) (4 6))

Given:

(define-syntax pop
  (syntax-rules ()
    [ (_ xs)
      (if (pair? xs)
        (begin0 (car xs) (set! xs (cdr xs)))
        #f) ] ))
(define-syntax Do-aux
  (syntax-rules (<> @)
    [(_ ((a b <>) d ...) (seen ...) z ...)
     (Do-aux (d ...) (seen ... (a b b)) z ...) ]
    [(_ ((a b c) d ...) (seen ...) z ...)
     (Do-aux (d ...) (seen ... (a b c)) z ...) ]
    [(_ ((a b) d ...) (seen ...) z ...)
     (Do-aux (d ...) (seen ... (a b)) z ...) ]
    [(_ ((a) d ...) (seen ...) z ...)
     (Do-aux (d ...) (seen ... (a '())) z ...) ]
    [(_ (a d ...) (seen ...) z ...)
     (Do-aux (d ...) (seen ... (a '())) z ...) ]
    [(_ () seen (a b ... @ xs) z ...)
     (Do-aux () seen (a b ... (reverse xs)) z ...) ]
    [(_ () seen till body ...)
     (do seen till body ...) ]))
(define-syntax Do
  (syntax-rules ()
    [(_ specs till body ...)
     (Do-aux specs () till body ...) ]))


-- 
[T]he problem is that lispniks are as cultish as any other devout group and
basically fall down frothing at the mouth if they see [heterodoxy].
  --- Kenny Tilton
The good news is, it's not Lisp that sucks, but Common Lisp. --- Paul Graham

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Subject: Re: Detele repeated in a list "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-09 10:23 +0000
  Re: Subject: Re: Detele repeated in a list "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-09 18:35 +0000
    Re: Subject: Re: Detele repeated in a list "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-09 18:43 +0000
      Re: Subject: Re: Detele repeated in a list "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-09 22:46 +0000
  Re: Subject: Re: Detele repeated in a list "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-28 15:36 +0000

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