If you want to form a matrix at the end, you'll need to keep the variables as numeric where "good" equals 1 and "bad" equals 0. That offers other benefits during analysis, too.
E = B > 0;
D=[A B E];
If you'd rather use strings,
E = cell(size(B));
E(B>0) = {'Good'};
E(B<0) = {'Bad'};
Then put it in a table
T = table(A,B,E);
