I suggest to use the current-pseudo-random-generator, because otherwise the
shuffle/seed will change globally the random sequence of all the program.
For example:
;---
#lang racket
;; shuffle/seed : list? integer -> list?
(define (shuffle/seed lst seed)
(random-seed seed)
(shuffle lst))
(define a-list (list 1 2 3 4 5 6 7 8 9 10))
(shuffle/seed a-list 0) ;=> '(3 4 9 8 5 1 10 7 6 2)
(random) ;=> 0.5029567011201275
(shuffle/seed a-list 0) ;=> '(3 4 9 8 5 1 10 7 6 2)
(random) ;=> 0.5029567011201275
(shuffle/seed a-list 1) ;=> '(3 2 1 8 5 10 4 7 6 9)
(random) ;=> 0.1591727701267079
(shuffle/seed a-list 1) ;=> '(3 2 1 8 5 10 4 7 6 9)
(random) ;=> 0.1591727701267079
(define (shuffle/temp/seed lst seed)
(parameterize ([current-pseudo-random-generator
(make-pseudo-random-generator)])
(random-seed seed)
(shuffle lst)))
(shuffle/temp/seed a-list 0) ;=> '(3 4 9 8 5 1 10 7 6 2)
(random) ;=> 0.9636171831359096 (may change)
(shuffle/temp/seed a-list 0) ;=> '(3 4 9 8 5 1 10 7 6 2)
(random) ;=> 0.6541579154005383 (may change)
(shuffle/temp/seed a-list 1) ;=> '(3 2 1 8 5 10 4 7 6 9)
(random) ;=> 0.679958229286436 (may change)
(shuffle/temp/seed a-list 1) ;=> '(3 2 1 8 5 10 4 7 6 9)
(random) ;=> 0.22302974490220356 (may change)
;---
[Note: shuffle/temp/seed is a horrible name. I used a different name to
avoid confusion.]
Gustavo
On Fri, Dec 2, 2016 at 5:37 AM, <meino.cra...@gmx.de> wrote:
> Daniel Feltey <dfel...@ccs.neu.edu> [16-12-02 09:28]:
> > I think something like this works:
> >
> > ;; shuffle/seed : list? integer -> list?
> > (define (shuffle/seed lst seed)
> > (random-seed seed)
> > (shuffle lst))
> >
> > > (define a-list (list 1 2 3 4 5 6 7 8 9 10))
> > > (shuffle/seed a-list 0)
> > '(3 4 9 8 5 1 10 7 6 2)
> > > (shuffle/seed a-list 0)
> > '(3 4 9 8 5 1 10 7 6 2)
> > > (shuffle/seed a-list 1)
> > '(3 2 1 8 5 10 4 7 6 9)
> > > (shuffle/seed a-list 1)
> > '(3 2 1 8 5 10 4 7 6 9)
> >
> >
> >
> > On Fri, Dec 2, 2016 at 2:05 AM, <meino.cra...@gmx.de> wrote:
> >
> > > Hi,
> > >
> > > is there a racket function, which shuffles a list of items
> > > based on a seed value...that is: Same seed value results in
> > > same shuffle results?
> > >
> > > Cheers
> > > Meino
> > >
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> HI Daniel,
>
> thanks a lot...exactly for what I have searched for!
>
> Cheers
> Meino
>
>
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