my $group1 = "group1";
my $group2 = "group1"; # using primary key again bw diff values
my $list1 = "1-2-3-4-5-6-7-8";
my $list2 = "1-2-3-4-5";

&test_hash($list1, $group1);
&test_hash($list2, $group2);

sub test_hash {
	my $list = $_[0];
	my $group = $_[1];
	my @vals = split /-/, $list;
	my %test_hash;
	$test_hash{$group} = $group;
	for (my $i = 0; $i < scalar @vals; $i++){
		$test_hash{$group}{$vals[$i]} = $vals[$i];
	}
	foreach $k(keys %test_hash){
		print "$k\n";
			foreach $v (keys %{ $test_hash{$k} }){
				print "\t$test_hash{$k}{$v}\n";
			}
	}
	
}

Output:
group1
        8
        6
        4
        1
        3
        7
        2
        5
group1 # 6,7,8 should not be in the new HoH below...
        8
        6
        4
        1
        3
        7
        2
        5