Assuming that shuffling is simple is a mistake, and yet once you see an unbiased algorithm on paper (or screen) you will probably say, "Oooh, I get it." But done wrong, shuffling can introduce bias, and it's easy to do wrong.

There is a nice article on Wikipedia: Fisher-Yates Shuffle. Implemented as a computer algorithm, it is sometimes known as the Knuth Shuffle. Also looking at the Pure Perl version of List::Util (here: Source for List::Util::PP) you will see a Perlish implementation of Fisher-Yates.

Another post here pointed you to perlfaq4, which shows another Fisher-Yates implementation that is easier to read than the List::Util::PP version.

For the masochistic or exceptionally curious: The Art of Computer Programming vol. 2 (3rd ed.), pg 145-146.

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