MATLAB: How to extract the first non-zero in several specific segments of the same matrix

Question

I'd like to find the first non-zero in several segments of the same large matrix.

For example: x = [3 2 3 4 5 6 6 8 6 10; 0 0 1 0 2 0 0 1 0 1]';

Now within x(1:3, 🙂 and x(7:10, 🙂 I'd like to extract the first non-zero in the second column and write out the corresponding value of the first column…no idea how…any help much appreciated. Patricia

Answer 1

ix1 = find(x(1:3,2),1,'first');  %index of first non-zero in x(1:3,2);
x1 = x(ix1,1);  %corresponding first-column value

ix2 = find(x(7:10,2),1,'first');  %index of first non-zero in x(7:10,2);
x2 = x(ix2,1);  %corresponding first-column value