how to use 2d matrix to index into 3d matrix

I have a 3-dimensional matrix C of size (m, n, k), and I have an index array ID of size (m,n) that indexes into the last dimension.

I tried indexing into it like this:

A = C(:,:,ID(:,:))

but that does not work. Is there a more compact way than the following function?

 function B = matindex(C, ID)
          B = zeros(size(ID));
          for i = 1:size(C, 1)
              for j = 1:size(C,2)
                  B(i,j) = C(i, j, ID(i,j));
              end
          end
  end

Thanks!

Answer 1

[Thorsten]

Use linear indexing

 N = size(C,1)*size(C,2); 
 idx  = [1:N]+(ID(1:N)-1)*N;
 B = reshape(C(idx), size(C,1), size(C,2));

[KAE]

What is the 2nd line of your code doing?