select category||type as grp, max(category) as cat, max(type) as typ,
       sum(quantity) as qty
from table
group by category || type

##</code><code>##

sub group_by {
    my ($rows, $group_keys) = @_;
    my @recs=();
    for my $row (@$rows) {
        push @recs, {
            GRP=>join(chr(28),@{$row}{@$group_keys}),
            %$row 
        };
    }
    return @recs;
}