On Mar 21, 3:58 pm, Ken Tilton <···········@optonline.net> wrote:
> (let* ((nums (list 0 1 2 3 4 5 6 7))
> (used (make-array (length nums)
> :element-type 'bit
> :initial-element 0)))
> (labels ((show-one (depth)
> (when (find 0 used)
> (let ((one (loop thereis
> (loop for n in nums
> unless (= 1(bit used n))
> when (zerop (random (length nums)))
> return n))))
> (print one)
> (setf (bit used one) 1)
> (show-one (1+ depth))))))
> (show-one 0)))
>
> This is somewhat distorted, but the labeled fn show-one is what I really
> have to do: given a mask and a list of numbers some of whom have already
> been "used" indicated by (= 1 (bit mask <that number>)), pick a number
> at random from those still unused. Without consing.
>
> In case it is confusing above, in reality there will be just a dozen
> random numbers under about 5000, and the mask will be a 5000 bit mask.
>
> All I have so far is trying numbers at random in a tight loop.
Arc:
(= nums '(9 22 37 54 61 78 83 92))
(= used '(22 54 83))
(= unused (rem [some _ used] nums))
(prn (random-elt unused))
In article
<····································@u72g2000hsf.googlegroups.com>,
William James <·········@yahoo.com> wrote:
> On Mar 21, 3:58 pm, Ken Tilton <···········@optonline.net> wrote:
> > (let* ((nums (list 0 1 2 3 4 5 6 7))
> > (used (make-array (length nums)
> > :element-type 'bit
> > :initial-element 0)))
> > (labels ((show-one (depth)
> > (when (find 0 used)
> > (let ((one (loop thereis
> > (loop for n in nums
> > unless (= 1(bit used n))
> > when (zerop (random (length nums)))
> > return n))))
> > (print one)
> > (setf (bit used one) 1)
> > (show-one (1+ depth))))))
> > (show-one 0)))
> >
> > This is somewhat distorted, but the labeled fn show-one is what I really
> > have to do: given a mask and a list of numbers some of whom have already
> > been "used" indicated by (= 1 (bit mask <that number>)), pick a number
> > at random from those still unused. Without consing.
^^^^^^^^^^^^^^^
> >
> > In case it is confusing above, in reality there will be just a dozen
> > random numbers under about 5000, and the mask will be a 5000 bit mask.
> >
> > All I have so far is trying numbers at random in a tight loop.
>
> Arc:
>
> (= nums '(9 22 37 54 61 78 83 92))
> (= used '(22 54 83))
He said that the used numbers are indicated with a bit mask, not a list.
>
> (= unused (rem [some _ used] nums))
> (prn (random-elt unused))
The assignment to unused appears to cons.
--
Barry Margolin, ······@alum.mit.edu
Arlington, MA
*** PLEASE don't copy me on replies, I'll read them in the group ***