Dynamic matrix columns combinations

Hello,

I would like to find all possible combinations of a matrix columns, with each column contribute a value, in each itteration of a loop. The matrix size changes in each itteration. For example:

A = [1 2 3

4 5 6

7 8 9].

should produce:

1 2 3

1 2 6

1 5 3 etc.

but should not produce:

1 4 2 for example.

My problems:

• When insert the matrix to combvec function nothing happens. The function accept vectors - and since I do it with different matrix size in each Itteration of a loop I can't write it manually.
• ndgrid also requires vectors - and since I need to choose a combination index in other variable - I'm not clear how this happens.
• I don't have combination function in my Matlab version.

Is there a way to define vectors dynamically in a loop? any idea on to how overcome this? Do I need to write a combination function myself?

[Stephen23]

"Is there a way to define vectors dynamically in a loop?"

What exactly do you mean?

Answer 1

[Stephen23]

"any idea on to how overcome this? Do I need to write a combination function myself?"

Use NDGRID with some comma-separated lists:

https://www.mathworks.com/matlabcentral/discussions/tips/847976-tutorial-comma-separated-lists-and-how-to-use-them

A = [1,2,3;4,5,6;7,8,9]

A = 3x3

1 2 3 4 5 6 7 8 9

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C = num2cell(A,1);
N = numel(C);
[C{:}] = ndgrid(C{:});
M = reshape(cat(1+N,C{:}),[],N)

M = 27x3

1 2 3 4 2 3 7 2 3 1 5 3 4 5 3 7 5 3 1 8 3 4 8 3 7 8 3 1 2 6

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[Stephen23]

If you really need just one combination on each loop iteration, then use the methods already described e.g.:

https://www.mathworks.com/matlabcentral/answers/623358-get-a-combination-of-unique-paths-for-given-pair-of-numbers#comment_1082638

Note that for large arrays you will have a very large number of combinations.