From: Pierre-Charles David <Pierre-Charles.David@...>
Date: 2001-10-09T17:49:31+09:00
Subject: [ruby-talk:22288] Re: [Newbie] Switching from Perl : suffling

Niklas Frykholm wrote:

> On Tue, Oct 09, 2001 at 04:58:24AM +0900, Dave Thomas wrote:
> 
>>How about something like
>>
>>     class Array
>>       def shuffle
>>         each_index {|i| o = rand(size); self[i], self[o] = self[o], self[i] }
>>       end
>>     end
>>


One of my teachers once showed me this method, which I find quite 
elegant (although perhaps not very efficient because of the arrays 
creation, but still O(n) ):

module Enumerable
   def shuffle
     # Associate a random number to each element
     pairs = self.collect { |item| [rand(), item] }
     # Sort the pairs according to the random part
     # and extract the original data
     (pairs.sort { |x, y| x[0] <=> y[0] }).collect { |pair| pair[1] }
   end
end

srand
a = (1..20).to_a
p a, a.shuffle

-- 
Pierre-Charles David (pcdavid <at> emn <dot> fr)
Computer Science PhD Student, �cole des Mines de Nantes, France
Homepage: http://purl.org/net/home/pcdavid