How can I count how many multi-dimension arrays in a matrix?

For example, I have a 10 by 2 matrix 'B' as below.

B=[1 9; 2 9; 4 8; 1 0; 1 0; 1 1; 1 3; 1 3; 1 2; 1 2]

I want to find out how many rows are 1 2 The answer should be 2. I am using for loop as shown below.

z=0;
for f1=1:10
    if B(f1,1)==1 && B(f1,2)==2
       z = z+1;
    end
end

This method works fine but when matrix 'B' gets bigger, it takes too much time. Is there any other ways to do this job?

Answer 1

[Andrei Bobrov]

z = nnz(ismember(B,[1 2],'rows'));

[Woojin Ahn]

Thank you! it works fine.