i have 16 different types of files and i have to take the files in the bunch of 2 from the 16 files, how i put permutation and combination to get 2 files from the 16 files each time differently?

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Sun Heat
Sun Heat 2018-8-7
评论： Sun Heat 2018-8-8
please keep in mind 1 and 2 is different combination and 2 and 1 is different combination.

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Guillaume
Guillaume 2018-8-7
Since there are only 240 combinations, it's trivial to generate them all as a 240x2 matrix:
allperms = nchoosek(1:16, 2);
allperms = [allperms; fliplr(allperms)];
You can then choose a row at random:
oneperm = allperms(randi(size(allperms, 1)), :)
or shuffle all the rows
allperms = allperms(randperm(size(allperms, 1)), :)
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Guillaume
Guillaume 2018-8-7
No, It does not extend to more than two elements. A generic version:
v = 1:16;
n = 4;
allperms = nchoosek(v, n); %all combinations
colperms = num2cell(perms(1:n), 2); %how many ways can we swap the columns
allperms = cell2mat(cellfun(@(p) allperms(:, p), colperms, 'UniformOutput', false)) %swap the columns all possible ways

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