How to vectorize row-wise diagonalization of a matrix

Question

I have an n-by-m matrix that I want to convert to a mn-by-m matrix, with each m-by-m block of the result containing the diagonal of each row.

For example, if the input i

Answer 1

It may not be the most computationally efficient solution, but here's a 1-liner using kron:

A = [1 2; 3 4; 5 6];
B = diag(reshape(A', 6, 1) * kron(ones(3, 1), eye(2))
% B = 
%     1     0
%     0     2
%     3     0
%     0     4
%     5     0
%     0     6

This can be generalized if A is n x m:

diag(reshape(A.', n*m, 1)) * kron(ones(n,1), eye(m))