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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp
Subject: Re: Remove part of a list
Date: Sat, 20 Jul 2024 16:23:20 -0000 (UTC)
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> > I have this list = '((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) (6 4) (7 4) (8 4)
> > (8 5) (9 5) (10 5))
> >
> > And i want to remove the part os list that begin in '(8 4) to
> > the '(8 4)..
> >
> > The result sould be this: = '((8 2) (8 3) (8 4) (8 5) (9 5) (10 5))
> 
> It looks as if the resulting sequence is the longest subsequence of
> the original sequence, in which the sums of the value pairs are
> strictly increasing.
> 
> 
> > Can anyone help me?
> 
> Maybe this?
> 
>   (defun strictly-increasing (input-pair-list)
>     (loop with max = nil
>           for pair in input-pair-list
>           for pair-value = (apply #'+ pair)
>           when (or (null max) (> pair-value max))
>             collect pair and
>             do (setf max pair-value))))

Testing in SBCL:

(defun strictly-increasing (input-pair-list)
  (loop with max = nil
        for pair in input-pair-list
        for pair-value = (apply #'+ pair)
        when (or (null max) (> pair-value max))
          collect pair and
          do (setf max pair-value))))

STRICTLY-INCREASING
*
debugger invoked on a SB-INT:SIMPLE-READER-ERROR in thread
#<THREAD "main thread" RUNNING {23EAC1B9}>:
  unmatched close parenthesis

(strictly-increasing
'((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) (6 4) (7 4) (8 4)
(8 5) (9 5) (10 5)))
  ===>
((8 2) (8 3) (8 4) (8 5) (9 5) (10 5))

Gauche Scheme

(define (strictly-increasing couples)
  (let1 n #f
    (filter
      (^c (let1 sum (apply + c)
            (and (or (not n) (> sum n)) (set! n sum))))
      couples)))

(strictly-increasing
  '((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) (6 4) (7 4) (8 4)
  (8 5) (9 5) (10 5)))

  ===>
((8 2) (8 3) (8 4) (8 5) (9 5) (10 5))