>> a = [1,2,3;1,2,4;5,6,7;5,6,8];
>> b = sortrows(a,3);
>> [~,idx] = unique(b(:,1:2),'rows','last');
>> b = b(idx,:)
b =
1 2 4
5 6 8
The sortrows call sorts rows by the third column (i.e. smaller values come before larger), then we select the unique rows (only columns 1 & 2), taking the last one each time (which because the rows are sorted will be the larger value in the third column).
