Re: [FWP] Probabilistic selection

[Sean McAfee <mcafee@umich.edu>]

Paul Makepeace <Paul.Makepeace@realprogrammers.com> wrote:
>I have a specification of link destinations and their weighted
>probabilities like so:
>
>	my %target = (
>    		'/:           _top'    => 1,
>    		'index.amyl:  _parent' => 3,
>    		'index.amyl:  _self'   => 15,
>    		'upload.amyl: _parent' => 1,
>	);

>In other words, you go to index.amyl in target="_parent" with
>probability 3 out of (1+3+15+1). The advantage of this scheme
>is that you don't have to make anything add up to 1.0 or use
>floating point, etc.

>I implemented this fairly straightforwardly as follows,
[snip]
>Any neater ways of doing this? Including perhaps, but not
>limited to, a different probabilities specification. I.e. any
>way of achieving the same goal.

Adapting the "choose a random line from a file" recipe from the Perl Cookbook:

my $total = 0;
while (my ($dest, $weight) = each %target) {
	$total += $weight;
	$where = $dest if rand($total) < $weight;
}

-- 
Sean McAfee                                                mcafee@umich.edu
print eval eval eval eval eval eval eval eval eval eval eval eval eval eval
q!q@q#q$q%q^q&q*q-q=q+q|q~q:q? Just Another Perl Hacker ?:~|+=-*&^%$#@!
-- 
Sean McAfee | GCS d->-- s+++: a28 C++ US+++ P+++$ L++ E- W+ N++ |
            | K w--- O? M- V-- PS+ PE Y+ PGP?>++ t+() 5++ X R+  | mcafee@
            | tv+ b++ DI++ D+ G e++ h r---* y+>++               | umich.edu

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