MATLAB: Generating an “all-combinations” matrix for a given vector

combinationvectors

Hi,
Given a column vector with integer values, say x = [2;3;4], I would like to create a 3*24 matrix of the following form
Each column in A is created by selecting 1st, 2nd and 3rd elements of the corresponding column from sets {1,2}, {1,2,3} and {1,2,3,4}, respectively. Thus, 2*3*4=24 different columns can be generated using this approach to form matrix A.
I am aware that the number of columns in matrix A grows very fast with the size of vector x and numeric values of its elements. But I won't be working with examples of matrix A larger than 500 cloumns.
Thanks for your help,
-burak

Best Answer

x = [2 3 4];
n = prod(x);
for i = 1:numel(x)
  li = []; for ii = 1:x(i), li = [li repmat(ii, [1 n/prod(x(1:i))])]; end, 
  A(i,:) = repmat(li, [1 n/numel(li)]);
end
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