MATLAB: Make zero some rows of a matrix

Question

It's neede to make zero those rows of a matrix that matrix(i,2) is 2 value less than matrix(1,2). 'matrix' has 2 column and 10000 rows. I wrote this but i don't know for what doesn't work

for i=1:size(r,1)
    if r(i,2)-r(1,2)<2
        r(i,2)=0;
    end
end

Answer 1

r(r(1,2)-r(:,2)>=2,:) = 0