Matrix column selection based on vector with indices

Hi all. I have a matrix of size m x n, with all entries as one at initialization. I also have a vector of size 1 x m. Each element is supposed to be between 1 and n, and the corresponding matrix entries are set to 0 (i.e. in the m-th matrix row, this is the column given by the m-th element of the vector). The code for that:

mask(sub2ind(size(mask),(1:numel(vector.'))',vector.')) = 0;

However, due to some modifications I had to make to the code, some elements of the vector can now take a value of 0, i.e. an invalid index. I would simply like to skip those elements. How can I do that?

Answer 1

[Torsten]

k=ones(6,4);
v=randi(size(k,2),1,size(k,1));
v(end) = 0

v = 1×6

3 2 2 2 1 0

idx = find(v>0)

idx = 1×5

1 2 3 4 5

k(sub2ind(size(k),idx,v(idx))) = 0

k = 6×4

1 1 0 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 1 1 1 1 1

Answer 2

[David Hill]

Why not just a simple loop?

k=ones(10,14);
v=randi(size(k,2),1,size(k,1));
for j=1:size(k,1)
    k(j,v(j))=0;
end

[Torsten]

According to the OP, there can be zeros in the v-vector:

k=ones(3,5);
v=randi(size(k,2),1,size(k,1));
v(end) = 0;
for j=1:size(k,1)
    if v(j) > 0
      k(j,v(j))=0;
    end
end
v

v = 1×3

2 5 0

k

k = 3×5

1 0 1 1 1 1 1 1 1 0 1 1 1 1 1

[Dominik Rhiem]

Hi, thanks for your answers! While that solves the problem, is there maybe a way to do that without a loop?