After typing this up, I see Zaxo already posted the same idea. Ah well, here it is anyway. 
#!/usr/bin/perl

use strict;

# Assign a weight to each item.  In this example
# pigs get twice the weight of dogs or cows
my %weight = (
        "dog" => 1,
        "cow" => 1,
        "pig" => 2
);

# Create an array with a number of elements
# equal to the weights of the items
my @bucket;
foreach my $animal (keys %weight)
{
        push @bucket, ($animal) x $weight{$animal};
}
# @bucket now looks like this:
#
# $bucket[0] = "dog"
# $bucket[1] = "cow"
# $bucket[2] = "pig"
# $bucket[3] = "pig"
#
# "pig" has twice as many slots as "dog" or "cow"

# The choose_weighted() subroutine now just has to
# pick a random element from the array.
sub choose_weighted
{
        my $bucket = shift;
        return $bucket->[rand(@$bucket)];
}

# Test code to demonstrate it works
my %count;
for (1..1000)
{
        my $animal = &choose_weighted(\@bucket);
        $count{$animal}++;
}

foreach my $animal (keys %count)
{
        print "$animal: $count{$animal}\n";
}

[download]

-Matt

In reply to Re: Weighted random numbers generator by DrManhattan
in thread Weighted random numbers generator by spurperl

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.