Combinations from a given set without repetition

Question

Suppose I have a matrix defined as follows

M = [C1 C2 C3 C4]

Where the C\'s are column vectors I want some efficient (i.e. no for loops) wa

Answer 1

This is the simplest way I've come up with:

n = size(M, 2);
[j, i] = ind2sub([n n], find(~triu(ones(n))));
ResultVec = M(:, [i j]);
ResultVec = reshape(ResultVec, [], 2)