From: Mathieu Bouchard <matju@...>
Date: 2001-05-08T14:10:38+09:00
Subject: [ruby-talk:14843] Re: How to do it the Ruby-way 3

On Tue, 1 May 2001, Stefan Matthias Aust wrote:

> Is there a similar built-in mehtod in Ruby?

no

> BTW, is there just one global random number generator?

i think so. Kernel#rand

>  It's of course easy to add (see below - code improvements are welcomed!),
>    def shuffle!
>      len = length
>      (0...len).each {|i|
>        j = rand len
>        self[i], self[j] = self[j], self[i]
>      }

Why this and not the following?

>        j = i + rand(len-i)

I'm not really good at probabilities, but it seems to me that the latter
makes a perfectly fair shuffler (given a perfectly fair rand()  function),
and that your "j = rand len" cannot make a perfectly fair shuffler,
because N**N is usually not divisible by factorial(N). It's nonetheless
possible that yours is very close to being a fair one; can you show me
that it is?

matju