Hi Samir,
On Thu, 26 Jun 2003 20:05:39 +0200, Samir Saidani <saidani at info.unicaen.fr> 
wrote:

> Here is a little piece of code to reproduce the bug:
>
> |s a|
> s_ Set new add: 'a'; add: 'b'; yourself.
> a_Random new.
> i_0.
> 500 timesRepeat: [ ((s atRandom: a)='a') ifTrue:[ i_i+1 ]. ].
> Transcript show: i; cr.

I have tow choices of a rewrite for Set>>atRandom:

(i) maybe abuses the Generator (asks for more than one random number)
and is unneccessarily recursive (i will smooth it out if you prefer this 
fix)
atRandom: aGenerator
	"Answer a random element of the receiver.  Uses aGenerator which
	should be kept by the user in a variable and used every time. Use
	this instead of #atRandom for better uniformity of random numbers 	because 
only you use the generator.  Causes an error if self has no 	elements."
	| answer |
	self emptyCheck.
	^(answer _ array at: (aGenerator nextInt: array size))
		ifNil:[self atRandom: aGenerator]
		ifNotNil:[answer]
(ii)can be more time-comsuming because it always iterates the whole set.
Especially in kryprographics this may be highly undesirable because
it makes it easy (given the knowledge of the implementation) to guess
the range of the random number from the time it took to produce it.
atRandom: aGenerator
	"Answer a random element of the receiver.  Uses aGenerator which
	should be kept by the user in a variable and used every time. Use
	this instead of #atRandom for better uniformity of random numbers 	because 
only you use the generator.  Causes an error if self has no 	elements."
	| rand |
	self emptyCheck.
	rand _ aGenerator nextInt: self size.
	self doWithIndex:[:each :ind |
		ind == rand ifTrue:[^each]]
	^ self errorEmptyCollection

HTH,
Torge

>
> Results (~100) show that you have 1/5 to have the first element.
>
> A workaround is to change a set as an array (probability is 1/2).
>
> |s a|
> s_ Set new add: 'a'; add: 'b'; yourself.
> a_Random new.
> i_0.
> 500 timesRepeat: [ ((s asArray atRandom: a)='a') ifTrue:[ i_i+1 ]. ].
> Transcript show: i; cr.
>
> Don't have time for the moment to fix it, but certainly due to the
> "array" representation of a set (Set(1,2) appears as an array of size
> 5 #(nil 1 2 nil nil nil).
>



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