

   DDeetteerrmmiinnee DDuupplliiccaattee EElleemmeennttss

        duplicated(x)

   VVaalluuee::

        This function determines which elements of a vector are
        duplicates of elements with smaller subscripts, and
        returns a logical vector indicating which elements are
        duplicates.

   SSeeee AAllssoo::

        `unique'.

   EExxaammpplleess::

        x <- c(9:20, 1:5, 3:7, 0:8)
        # extract unique elements
        x[!duplicated(x)]
        all(0:20  == sort(x[!duplicated(x)]))

