

   EExxttrraacctt UUnniiqquuee EElleemmeennttss

        unique(x)

   DDeessccrriippttiioonn::

        `unique' returns a vector like `x' but with duplicate
        elements removed.  If an element is equal to one with a
        smaller index, it is removed.

   SSeeee AAllssoo::

        `duplicated' which gives the indices of duplicated ele-
        ments.

   EExxaammpplleess::

        unique(c(3:5, 11:8, 8 + 0:5))
        length(unique(sample(100,100,replace=T)))# ~= 100(1 - 1/e) = 63.21
        my.unique <- function(x) x[!duplicated(x)]
        for(i in 1:4) { x <- rpois(100, pi); print(all(unique(x) == my.unique(x))) }

