From: Kero <kero@...>
Date: 2005-12-05T05:32:33+09:00
Subject: Re: need some Ruby magic

> How about just doing this?
>
> class Array
>    def shuffle
>      newarr = self
>      self.length.times do |x|
>        y = rand(self.length)
>        newarr[x], newarr[y] = newarr[y], newarr[x]
>      end
>      newarr
>    end
> end
>
> shuffled_array = my_array.shuffle

"Just" doing that
1) changes the receiver (use new_arr = self.dup instead)
2) definitely has a bias. Look e.g. at an array of length three. You will
   first swap the first element with 3 possibilities, then the second and so
   on; you're going through 3**3 possibilities. There are 3! possible
   permutations, but alas, 3! == 6 is not a perfect divisor of 3**3 == 27,
   thus you have a bias.