R: Determine Duplicate Elements

duplicated {base} | R Documentation

## Determine Duplicate Elements

### Description

Determines which elements of a vector of data frame are duplicates of elements with smaller subscripts, and returns a logical vector indicating which elements (rows) are duplicates.

### Usage

    duplicated(x, incomparables = FALSE)

### Arguments

`x` | an atomic vector or a data fram.e
`incomparables` | a vector of values that cannot be compared. Currently, `FALSE` is the only possible value, meaning that all values can be compared.

### Details

This is a generic function with methods for vectors and data frames. The data frame method works by pasting together a character representation of the rows separated by `\r`, so may be imperfect if the data frame has characters with embedded carriage returns or columns which do not reliably map to characters.

### See Also

`unique`.

### Examples

    x <- c(9:20, 1:5, 3:7, 0:8)
    ## extract unique elements
    (xu <- x[!duplicated(x)])
    stopifnot(xu == unique(x), # but unique(x) is more efficient
              0:20 == sort(x[!duplicated(x)]))

    data(iris)
    stopifnot(duplicated(iris)[143] == TRUE)

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