# fill %allfriends with all friendids and cut $friends
        # down to only include those that match $filter
        my %allfriends = ();
        foreach my $fid (keys %$friends) {
            $allfriends{$fid}++;

            # delete from friends if it doesn't match the filter
            next unless $filter && ! ($friends->{$fid}->{'groupmask'}+0 & $filter+0);
            delete $friends->{$fid};
        }