There's a much more efficient way if you know the total weight in advance (or calculate it): 
use List::Util qw(sum);
my $total = sum values %$group;
my $picked;
for (keys %$group){
    if (rand() < $group->{$_} / $total){
        $picked = $_;
        last;
    }
    # update: I forgot this line:
    $total -= $group->{$_};
    # without this line items later in the hash are chosen
    # too seldom, and you might chose none at all. Very bad.
}

[download]

I somehow think it's not entirely fair, but I can't get a straight thought on stochastic at this time (0:30 AM here), maybe I can think of a prove (or disprove) tomorrow.

In reply to Re: Weighted random selection by moritz
in thread Weighted random selection by cosmicperl

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