MATLAB: How to create 2D matrix from 3D without a loop

Question

I have an n x m x 3 matrix A and an n x m matrix B. B contains the values 1, 2, or 3, referring to the three different layers in A. I want to create another n x m matrix C where each point is the value of A from the layer specified by B. For instance, if A(1,1,:) = [8 6 5], B(1,1) = 2, then C(1,1) = 6, because B at that point specifies taking from the second layer. I know how to do this with a loop, but I was wondering if there was an easier, vectorized way to do so. Thanks!

Answer 1

[n,m,k] = size(A);
[i,j] = ndgrid(1:n,1:m);
C = A(sub2ind([n,m,k],i,j,B);