categorical indices in for loop

I have different sets with categorical data in them and I want to use them in for loop. Below is an example:

S = {'S1'; 'S2'}; T = {'T1'; 'T2'}; N = union(S,T);

Then I need to use i index in set of N once and in set of S in another for loop. I mean instead of for i= 1:n I need to say something that the for loop understands that i should only be in set S or in set N. I hope my question is clear. How can I do that? I appreciate any help on this.

[Amir Xz]

Try this:

for i=N

[Sarah Ansari]

Thank you for your help. I have another issue then. I nee to do some operation on the indices then but it gives error as the indices are not numbers anymore. Do you have any suggestion?

for i = N for j = N model.obj(i+(j-1)*n) = distance(i,j); end end

[Walter Roberson]

for i=1:length(S)
  for j=1:length(T)

[Amir Xz]

When you write:

S = {'S1'; 'S2'};

S has two characters : 'S1' and 'S2'

But you said "I have different sets with categorical data".

The question is: Are S1 and S2 set of numbers and you wanted to group them as S? Or just really two char as 'S1' & 'S2'?

Please, give more details about S1, S2, T1 and T2.