Re: [FWP] Probabilistic selection

[Steve Lane <sml@zfx.com>]

Paul Makepeace 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,
> 
>     my $sum = 0; $sum += $_ for values %target;
>     my $which = rand $sum;
>     my $where;
>     $sum = 0;
>     for my $href (keys %target) {
>         if ($which < ($sum += $target{$href})) { $where = $href; last }
>     }
> 
> 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.

i don't know about "neater", but here's another way:

my %target = (
  '/:           _top'    => 1,
  'index.amyl:  _parent' => 3,
  'index.amyl:  _self'   => 15,
  'upload.amyl: _parent' => 1,
);

my @keylist = map { ($_) x $target{$_} } keys %target;
my $key = $keylist[rand @keylist];
--
Steve Lane <sml@zfx.com>

==== Want to unsubscribe from Fun With Perl?  Well, if you insist...
==== Send email to <fwp-request@technofile.org> with message _body_
====   unsubscribe