Filter matrix rows depending on values in a second matrix

Question

Given a 2x3 matrix x and a 4x2 matrix y, I\'d like to use each row of y to index into x. If the value in x i

Answer 1

>> x = [1, 2, 3; -1, 2, -1];
>>y = [1, 1; 
    1, 2; 
    1, 3; 
    2, 1;
    2, 2;
    2, 3];
>>row_idx = reshape((x == -1)',1,6);
>>y = y(row_idx,:);

I think you didn't include all the index of x in y. I included all of them in y. Have a look..

Generalized version:

>> x = [1, 2, 3; -1, 2, -1];
>>y = [1, 1; 
    1, 2; 
    1, 3; 
    2, 1;
    2, 2;
    2, 3];
>>row_idx = reshape((x == -1)',1,size(x,1)*size(x,2));
>>y = y(row_idx,:);