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Incredible shrinking list....
From: |
Scott |
Subject: |
Incredible shrinking list.... |
Date: |
Fri, 17 Oct 2008 14:47:42 -0600 |
User-agent: |
Mutt/1.5.16 (2007-06-09) |
Hi,
I am very much a newbie, so forgive if this is a stupid question.
I am trying to write a function which returns a randomized permutation
of a certain number of items. Here is my stab at it, and the problem
which baffles me:
(defun pick-ten ()
"Pick a series of ten unique random numbers from 0-9.
You should ensure that random is properly 'seeded', as eg:
(random t)
prior to using this function."
(let ((all-ten '(0 1 2 3 4 5 6 7 8 9)) ;initial list
(rnd-list '()) ;return value
(nxt 0)) ;placeholder for current number
(while all-ten ;step through the list
(setq all-ten ;trim by
(delq ;deleting selected number
(setq nxt ;but remember number for later
(car
(nthcdr (mod (random)(length all-ten)) all-ten)
)
) all-ten))
(setq rnd-list (cons nxt rnd-list)) ;and put into the return value
)
rnd-list ;now return it.
))
;; works fine on the first evaluation,
;; but the series somehow shrinks with subsequent calls!
;; what am I doing wrong???!
;;
(pick-ten)(3 2 9 7 1 6 0 5 8 4)
(pick-ten)(1 0 2 3)
(pick-ten)(0 1)
(pick-ten)(0)
(version)"GNU Emacs 21.3.2 (i586-pc-linux-gnu, X toolkit)
of 2004-07-02 on DrMemory"
(time-to-upgradep (version))t
I'm sure there is a far better way to write this, but I can't for the
life of me figure out why my ham-handed attempt is acting so
bizarrely, and would appreciate any help!
thanks,
Scott swanson
- Incredible shrinking list....,
Scott <=