How to create matrix of all combinations?

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Mr M. on 27 Jul 2018
Commented: Matt J on 23 Aug 2018
Suppose I have variables x1, x2, x3. x1 can be any element of the set {1,2,3}, x2 can be {1,2,3,4,5} and x3 can be {10,11,12,13,14,15} for example. How to create the matrix of all combinations, in which each row is a possible combination: [3,4,12] for example. Is it possible to do it without a for cycle with some tricks?
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Answers (2)

Patrick Zwierzynski on 27 Jul 2018
Edited: Patrick Zwierzynski on 27 Jul 2018
If you change x1, x2, and x3 to be vectors instead of sets, you can use the "combvec" function and simply call "combvec(x1, x2, x3)". You can then use the column indices of the resulting matrix to select the different combinations.
Here's the link to the documentation: https://www.mathworks.com/help/nnet/ref/combvec.html
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Mr M. on 27 Jul 2018
Unfortunately I do not have the necessary toolbox for combvec

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Bruno Luong on 27 Jul 2018
c={[1 2 3],[1 2 3 4 5],[10 11 12 13 14 15]}
[c{:}]=ndgrid(c{:});
n=length(c);
c = reshape(cat(n+1,c{:}),[],n)
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Matt J on 23 Aug 2018
Not slower than it should be. If you have many combinations, then naturally it will take a long time.

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