This help topic is for R version 0.60. For the current version of R, try https://stat.ethz.ch/R-manual/R-patched/library/base/html/duplicated.html
duplicated {base}R Documentation

Determine Duplicate Elements

Usage

duplicated(x)

Value

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.

See Also

unique.

Examples

x <- c(9:20, 1:5, 3:7, 0:8)
# extract unique elements
x[!duplicated(x)]
all(0:20  == sort(x[!duplicated(x)]))
[Package base version 0.60 ]