From: Joerg Plate <Plate@...>
Date: 2001-10-09T09:42:52+09:00
Subject: [ruby-talk:22268] Re: [Newbie] Switching from Perl : suffling


This is a Fisher-Yates-Shuffle
>> | sub shuffle {
>> |   srand;
>> |   my $array = shift;
>> |     for (my $i = @$array; --$i > 0; ) {
>> |       my $j = int rand ($i+1);
>> |       @$array[$i,$j] = @$array[$j,$i];
>> |   }
>> | }

This is not the Fisher-Yates-Shuffle (and a biased algorithm
according to the Perl Cookbook...)

>      class Array
>        def shuffle
>          each_index {|i| o = rand(size); self[i], self[o] =
>          self[o], self[i] }
>        end

What about the following?

class Array
  def shuffle
    last = self.size
    each_index {
      |i|   j=last-i;
            k=rand(last)+1;
            self[i], self[o] = self[o], self[i] }
  end

-- 
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