#!perl
#
# farm.pl

use strict;
use warnings;

# Lookup table of farm animals by home
my %home_of = (
    Cat     => 'House',
    Cow     => 'Field',
    Dog     => 'Yard',
    Goat    => 'Barn',
    Hamster => 'House',
    Hen     => 'Coop',
    Horse   => 'Barn',
    Sheep   => 'Barn',
    Pig     => 'Sty',
    Rooster => 'Yard',
);

my %animals_by;

# Add each animal to a list of farm animals by home...
while (my ($animal, $home) = each %home_of) {
    push @{ $animals_by{$home} }, $animal;
}

# Print ordered lists of animals by an ordered list of homes...
for my $home (sort keys %animals_by) {
    my $list_of_animals = join ', ', sort @{ $animals_by{$home} };

    print "$home\t$list_of_animals\n";
}

__END__
Barn    Goat, Horse, Sheep
Coop    Hen
Field   Cow
House   Cat, Hamster
Sty     Pig
Yard    Dog, Rooster