my @non_duplicates = do{
    #lets use a hash since we want unique values
    #and localize it so its a fresh copy
    local %_;

    #undef the values of this localized hash
    #while assigning your values as keys
    undef @_{@{$map{$$row[1]}{$$row[2]}}};

    #call keys on the hash to get a list of your
    #unique values
    keys %_;
}
#assign our unique list back to your original structure.
$map{$$row[1]}{$$row[2]} = \@non_duplicates;