DeleteDuplicates
[list]DeleteDuplicates
[list, test]True
on pairs of elements.
DeleteDuplicates
does not change the order of the remaining elements.
DeleteDuplicates[{1, 7, 8, 4, 3, 4, 1, 9, 9, 2, 1}]
DeleteDuplicates[{3,2,1,2,3,4}, Less]