how to generate possible distinct sets of pairs from a given set?

问题

in matlab how do I do this? I have a set of n elements

from this set I make a new set of n/2 pairs such that elements in different pairs are distinct. how do I generate distinct sets of such n/2 pairs from n elements in matlab?

e.g. input set - {1,2,3,4}

possible output sets -

{{1,2},{3,4}}

{{1,3},{2,4}}

{{1,4},{2,3}}

回答1:

I could not find a clean solution for the "distinct elements for each halved-vector" requirement. Thus I suggest to check each result individually. I expect that there's a better solution around: this one just does its job.

x = [1 2 3 3];
xsize = size(x,2);

p = perms(x);
up = unique(p,'rows');

result = [];

for entry=up'
  left = entry(1:xsize/2);
  right = entry(xsize/2+1:xsize);
  if numel(unique(left)) == xsize/2 && numel(unique(right)) == xsize/2
    result = vertcat(result,entry')
  end
end

Just for completeness, the result is:

1   3   2   3
1   3   3   2
2   3   1   3
2   3   3   1
3   1   2   3
3   1   3   2
3   2   1   3
3   2   3   1

I was not sure if you needed to actually split the halved vectors. In that case, just put left and right into whatever you prefer.

来源：https://stackoverflow.com/questions/10976347/how-to-generate-possible-distinct-sets-of-pairs-from-a-given-set