### 4.18.3. Discussion

Shuffling is a surprisingly tricky process. It's easy to write a bad
shuffle:

sub naive_shuffle { # DON'T DO THIS
for (my $i = 0; $i < @_; $i++) {
my $j = int rand @_; # pick random element
($_[$i], $_[$j]) = ($_[$j], $_[$i]); # swap 'em
}
}

This algorithm is biased; the list's possible permutations don't all
have the same probability of being generated. The proof of this is
simple: take the case where we're passed a three-element list. We
generate three random numbers, each of which can have three possible
values, yielding 27 possible outcomes. There are only six
permutations of the three-element list, though. Because 27 isn't
evenly divisible by 6, some outcomes are more likely than others.

The List::Util module's `shuffle` function avoids
this bias to produce a more randomly shuffled result.

If all you want to do is pick one random element from the array, use:

$value = $array[ int(rand(@array)) ];