unique(x)
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.duplicated which gives the indices of duplicated elements.
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))) }