MATLAB: Count vector position in a matrix

Question

Hi all. I need an algorithm, which takes my first element (! = 0) from an array and checks that element in a vector that already contains the elements of the matrix (! = 0) and begins to count the position it is in. Once it has found the respective element, it adds its position in another vector.

Ex: I have A = [ 2 3 4 0;

8 7 0 0;

2 0 1 3]

VectorA= [ 2 3 4 8 7 2 1 3] (elements != 0)

rowptr = [1 4 6]

Explain:

2 is in position 1 in the vectorA -> rowptr = [ 1

8 is in position 4 in the vectorA -> rowptr = [ 1 4

2 is in position 6 -> rowptr = [1 4 6]

A little help, please!

Answer 1

Here's one way:

tmp = cumsum(sum(A~=0,2))
rowptr = [1; tmp(1:end-1)+1];