From: seebs@... (Peter Seebach)
Date: 2007-04-30T11:28:35+09:00
Subject: Re: sorting by rand?

In message <40D2708E-0D0C-42E4-82B3-E31D93481880@mac.com>, Gary Wright writes:
>
>On Apr 29, 2007, at 10:01 PM, Peter Seebach wrote:
>> So, two vaguely related questions:
>> 1.  Is there a reasonably sane way to do this, should I ever find
>> myself wanting one?
>
>Short answer:   array.sort_by { rand }
>
>Longer answer: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby- 
>talk/168963

Well, okay.  It works in practice.  Is it guaranteed to work, and is
it actually reasonable to expect the output to be randomly shuffled?

Just for comparison, I tried:

l = a.length
a.each_index { |x| a[x] = a[rand(l)] }

I'm pretty sure I got the generic shuffle algorithm right (Knuth FTW),
and if so, it produces quality random results in about 1/4 the time.

-s