matrix - matlab - how to merge/interlace 2 matrices?

Question

How can I combine 2 matrices A, B into one so that the new matrix C = row 1 of A, followed by row 1 of B, then row 2 of A, row 2 of B, row 3 of A, row 3 of B, etc? Preferably without a for loop?

ex: A = [1 2 3; 4 5 6], B = [5 5 5; 8 8 8].
AB = [1 2 3; 5 5 5; 4 5 6; 8 8 8].

Answer 1

All you need is a bit of catenation and reshaping. First, you catenate along dimension 2, then you transpose, and linearize (AB(:)), so that you get a vector whose first three elements are the first row of A, then the first row of B, then the second row of A, etc. All that's left in the end is calling reshape to put everything back into an array again.

nColumns = size(A,2);
AB = [A,B]'; 
AB = reshape(AB(:),nColumns,[])'; 

Alternatively, you can construct AB directly via indexing. In this case, A is allowed to have one more row than B. This is probably faster than the above.

[nRowsA,nCols] = size(A);
nRowsB = size(B,1);

AB = zeros(nRowsA+nRowsB,nCols);
AB(1:2:end,:) = A;
AB(2:2:end,:) = B;