how can I generate different vectors with the all the unique combinations of numbers inside a one vector?

Hi, If i have a vector a like:

    a=[1 2 3 4]:

how can I generate different vectors with the all the unique combinations of the original numbers like:

r=[1 2 3]
r=[1 2 4]
r=[2 3 4]
r=[1 2]
r=[1 3]
r=[1 4]
r=[2 3]
r=[2 4]
r=[3 4]
r=[1]
r=[2]
r=[3]
r=[4]

Answer 1

[Andrei Bobrov]

a=[1 2 3 4]
r = cell;
for ii = numel(a)-1:-1:1
    r = [r;num2cell(nchoosek(a,ii),2)];
end

[German Preciat Gonzalez]

Thanks,

just a comment

r={}