Generating Hash-of-List using map?

[cmv]

Hi Monks-

I don't quite understand why this one is so hard for me to figure out - please help!

This code:

use warnings;
use strict;
use Data::Dumper;

my @CELLS=( 'A-1', 'A-2', 'A-3', 'A-4', 'B-5', 'B-6', 'C-7', 'C-8');

my %hash=map { /^(.*)-(\d+)$/; $1=>$2} @CELLS;

print STDERR "hash DUMPER:\n", Dumper(\%hash), "\n";

Generates a Hash whose key is the alphabetical letter found before the dash, and whose value is the last numerical digit found for that letter

hash DUMPER:
$VAR1 = {
          'A' => '4',
          'C' => '8',
          'B' => '6'
        };

How can I change the map command so that it will generate a list of all the numerical digits found? Something like this:

hash DUMPER:
$VAR1 = {
          'A' => [
                   1,
                   2,
                   3,
                   4
                 ],
          'C' => [
                   7,
                   8
                 ],
          'B' => [
                   5,
                   6
                 ]
        };

Thanks

-Craig