From: Neil Spring <nspring@...>
Date: 2004-12-16T02:05:42+09:00
Subject: Re: [ANN] rand.rb 0.9: Random access methods for Enumerables

On Dec 14, 2004, at 7:24 PM, Ilmari Heikkinen wrote:
> rand.rb is a library for picking random elements and shuffling.
> This work is licensed under the same terms as Ruby itself.

umm,  could you maybe replace:

   def shuffle!
     sort!{rand <=> 0.5}
   end

with:

   def shuffle!
     each_index {|j| i = rand(size-j); self[j], self[j+i] = self[j+i], 
self[j]}
     self
   end

I would not rely on sort to do the right thing, and it is less 
efficient than necessary.  I use the second shuffle code extensively in 
my code which deals with shuffling lots and lots of elements.  
Presumably the second is O(n) where the sort based scheme is at best 
O(n log n).  A little googling suggests this is the "Fisher-Yates 
shuffle."

-neil