unique                 package:base                 R Documentation

Extract Unique Elements

Description:

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

Usage:

     unique(x, incomparables = FALSE)

Arguments:

       x: an atomic vector or a data frame.

incomparables: a vector of values that cannot be compared. Currently,
          `FALSE' is the only possible value, meaning that all values
          can be compared.

See Also:

     `duplicated' which gives the indices of duplicated elements.

Examples:

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

     data(iris)
     unique(iris)
     stopifnot(dim(unique(iris)) == c(149, 5))

