How to I combine different numbers of columns from two matrices?

I have two matrices, A and B, and would like to generate a third matrix, C, that contains column 1 of A followed by columns 1:3 of B, then column 2 of A followed by columns 4:6 of B, and so on, until the end of matrix A is reached. I know I can individually generate each group of [A(:,x),B(:,x:x+2)] and then concatenate them, but I'd like to make one loop function to read matrices of any size.

Answer 1

[Mohammad Abouali]

No loop is needed. Check this:

% Sample A and B
A=repmat(1:4,3,1); % A has its column filled with number 1 to 4
A =
     1 2 3 4
     1 2 3 4
     1 2 3 4

B=repmat(5:16,3,1); % B has its column filled with number 5 to 16 
B =
     5 6 7 8 9 10 11 12 13 14 15 16
     5 6 7 8 9 10 11 12 13 14 15 16
     5 6 7 8 9 10 11 12 13 14 15 16

nColA=size(A,2);
if (size(B,2)<(nColA*3))
  error('B does not have enough column');
end
if (size(B,1)~=size(A,1))
  error('A and B must have same number of rows');
end

% Initializing C
C=NaN(size(A,1),nColA*4);

% PLacing A in C
C(:,((1:nColA)-1)*4+1)=A;

% Placeing B in C
C(:,(1:nColA*3)+floor(((1:nColA*3)-1)/3)+1)=B;

C =
     1 5 6 7 2 8 9 10 3 11 12 13 4 14 15 16
     1 5 6 7 2 8 9 10 3 11 12 13 4 14 15 16
     1 5 6 7 2 8 9 10 3 11 12 13 4 14 15 16

[PBB]

Worked perfectly. Thanks!

[Mohammad Abouali]

You are welcome

Answer 2

[Guillaume]

I would have done it with a logical array:

A=repmat(1:4,3,1); % A has its column filled with number 1 to 4
B=repmat(5:16,3,1); % B has its column filled with number 5 to 16 

filler = repmat(logical([1 0 0 0]), size(A)); %logical array. 1 indicates use A, 0 indicates use B.
C = zeros(size(filler)); %output array
C(filler) = A; %fill 1 with A
C(~filler) = B %fill 0 with B

Simpler than calculating column indices.