[REBOL] Re: random string
From: joel:neely:fedex at: 11-Apr-2002 6:15
Hi, Andrew,
Andrew Martin wrote:
> John wrote:
> > Is there a better way of creating a random string of 8
> > characters...
>
> How about:
>
> Allowed_Characters: "ABCDEF123"
> copy/part random Allowed_Characters 8
>
That produces a random permutation from "ABCDEF123", *not*
a string of characters each drawn from "ABCDEF123". IOW a
much smaller sample space, since e.g. the result of
>> loop 8 [append "" random/only allowed_characters]
== "CD1AC3DB"
could never appear (due to the duplicated appearance of
the #"D").
If C is then number of candidate characters and W is the
desired string width, then we're dealing with
C! / (C-W)!
possibilities for "copy/part ..." versus
C ** W
for "append ... random ..." which, for the sample above,
means only
>> 2 * 3 * 4 * 5 * 6 * 7 * 8 * 9 == 362880
possible permutations, but
>> 9 * 9 * 9 * 9 * 9 * 9 * 9 * 9 == 43046721
possible "fair random with replacement" selections.
-jn-
--
; Joel Neely joeldotneelyatfedexdotcom
REBOL [] do [ do func [s] [ foreach [a b] s [prin b] ] sort/skip
do function [s] [t] [ t: "" foreach [a b] s [repend t [b a]] t ] {
| e s m!zauafBpcvekexEohthjJakwLrngohOqrlryRnsctdtiub} 2 ]
