x = [ 1 5 6 7 8 3 2 ];
y = [ 2 9 4 6 4 5 6 ];
idx = find(x > 3); % Returns the indexes where x is larger than 3
plotregression(x(idx), y(idx)); % Only uses the indexes of the vectors, where x were larger than 3
Replace with other regression methods, depending on what you need.
