Seek_Knowledge:

If you're interested in the unique values, I'd suggest adding another level to your hash, something like:

use strict; use warnings;
my %hash;
while (<DATA>) {
    s/\s+$//;
    my ($key1, $key2) = split /\s+/, $_;
    $hash{$key1}{$key2}++;
}
for my $k1 (sort keys %hash) {
    print "$k1: ", join(", ", sort keys %{$hash{$k1}}), "\n";
}
__DATA__
Lemon Juice
Lemon Cake
Apple Cider
Lemon Cake
Apple Butter
Apple Sauce
Apple Juice
Lemon Juice
[download]

Note: The code is untested, but I'd expect output like:

Apple: Butter, Cider, Juice, Sauce
Lemon: Cake, Juice
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.