How to extract a vector from a vector given a reference vector ?

I have a main vector = [1 1 1 1 2 3 4 5 7 8 8 8 2 2 1 1 1 .....] and a reference vector = [1 3 4 7 9 1312] how do i extract the vector in main whose value are in reference vector ?

so it should be [1 1 1 1 3 4 7]

Answer 1

[KSSV]

A = [1 1 1 1 2 3 4 5 7 8 8 8 2 2 1 1 1]  ;
B = [1 3 4 7 9 13 12] ;

iwant = A(ismember(A,B))