Actually, even this is problematic. Because you need to go through the list in a defined order to ensure that each item has its respective probabilities. So you really do need the array refs ... but you need them in a list, not a hash.

my @items = (
    ["foo", 1],
    ["bar", 3],
    ["baz", 4],
    ["quux", 9]
);

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Then, when you generate a number, you first loop through summing $_->[1]: 
  use List::Util;
  my $total_weight = List::Util::sum(map { $_->[1] } @items);

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and then you generate a number from that, and then find the item in the total: 
  my $pick = int(rand($total_weight));
  my $picked_item = (List::Util::first { $pick -= $_->[1]; $pick < 0 }
+ @items)->[0];

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Ok, that's a bit convoluted, but I don't quite want to do someone's homework ;-) Anyway, the point is that if, when iterating over the hash, you end up with the hash being reordered from lookup to lookup, I don't think you'll get precisely the correct distribution. (Of course, I'm assuming a perfectly random rand function, but that is a separate problem.)

Update: fix some minor formatting, and off-by-one error (was $pick <= 0)

In reply to Re^3: Picking a random item through probability by Tanktalus
in thread Picking a random item through probability by muba

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