Filtering data from Struct in Matlab

Question

S.o     = [{\'A\'} ,{\'B\'}, {\'C\'}];
S.p.q   = [{\'q1\'}, {\'q2\'}, {\'q3\'}];
S.p.q.a = [-1,-2,-3];
S.p.q.b = [10,20,30];

How do i create another str