How to find the indices of nonzero rows in a matrix?

Question

How to find the indices of nonzero rows in a matrix?

Example:

A = [
       14  0  6  9  8  17
       85 14  1  3  0  99
       0   0  0  0  0   0 
           


        

Answer 1

You can use

   ix = any(x,2);

any check whether there is any element that is not a zero. The second argument stands for "per-row" computation.

If you want to get the numeric index, you can use find function:

   numIx = find(ix);

---

Another method:

  ix = sum(abs(x),2)~=0;

Answer 2

Use

[i,~] = ind2sub(size(A),find(A));

v = unique(i);

Result for the matrix given above:

v = unique(i')

v =

     1     2     4     6

Answer 3

Here's one that ab(uses) the fast matrix multiplication in MATLAB -

idx = find(abs(A)*ones(size(A,2),1))