how to replicate an array

Question

I want to make a function like this

>> matdup([1 2],3,4)            %or any other input that user wish to enter
ans= 

 1     2     1     2     1     2         


        

Answer 1

Method 1: Are you allowed to use ones? Try this -

A = [1 2]

rowIdx = [1 : size(A,1)]';
colIdx = [1 : size(A,2)]';

out = A(rowIdx(:, ones(3,1)), colIdx(:, ones(4,1)))

Output

out =

     1     2     1     2     1     2     1     2
     1     2     1     2     1     2     1     2
     1     2     1     2     1     2     1     2

Method 2: Are you allowed to use bsxfun and permute? Try this for the same result -

A = [1 2]
row_mapped = bsxfun(@plus,A,zeros(3,1))
out = reshape(bsxfun(@plus,row_mapped,permute(zeros(4,1),[3 2 1])),[3 8])

Answer 2

Matlab has a funcion called repmat that does the same.

If you want to create a similar function, you could do something like this:

function B = matdup(A, M, N)
    [nr, nc] = size(A);
    B = zeros([nr nc] .* [M N]);
    for r = 1:M
        for c = 1:N
            rr = (r - 1) * nr + 1;
            cc = (c - 1) * nc + 1;
            B(rr:rr + nr - 1, cc:cc + nc - 1) = A;
        end
    end
end

Note this function is restricted to 2D matrices.

Answer 3

The replication can be done easily using mod:

function R = matdup(A, M, N)
    [m n]= size(A);
    R = A(mod(0:m*M-1,m)+1, mod(0:n*N-1,n)+1)

Answer 4

Try kron:

matdup = @(x,m,n) kron(ones(m,n),x)

Demonstration:

>> A = [5 6 7];
>> out = matdup(A,3,2)
out =
     5     6     7     5     6     7
     5     6     7     5     6     7
     5     6     7     5     6     7

---

Note that you can switch the inputs to kron to effectively replicate elements rather than the whole matrix:

repel = @(x,m,n) kron(x,ones(m,n));

Demonstration:

>> A = [5 6 7];
>> out = repel(A,3,2)
out =
     5     5     6     6     7     7
     5     5     6     6     7     7
     5     5     6     6     7     7