How to convert matrix to a stack of diagonal matrices based on every row?

Question

I have a matrix:

A = [1 1 1
     2 2 2
     3 3 3]

Is there a vectorized way of obtaining:

B = [1 0 0 
     0 1 0
     0 0          


        

Answer 1

This code converts A to a cell array of row vectors, applies the diag function to each, and then stacks them:

D = cellfun(@diag,mat2cell(A, ones(size(A,1), 1), size(A,2)), 'UniformOutput', false);
B = vertcat(D{:});

Results:

B =

     1     0     0
     0     1     0
     0     0     1
     2     0     0
     0     2     0
     0     0     2
     3     0     0
     0     3     0
     0     0     3