R: Extract Unique Elements

unique {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))

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