Use the 2nd output of findgroups:
A = [1,1; 1,2; 2,2; 3,3; 3,4; 1,3; 1,2];
[G, ID1, ID2] = findgroups(A(:, 1), A(:, 2));
AG = [ID1, ID2];
Now the i.th row of AG contains the 2 column values of the i.th group of G.
AG(3, :)
I assume unique('rows') is more efficient here.
