R: Make Character Strings Unique

make.unique {base} | R Documentation

## Make Character Strings Unique

### Description

Makes the elements of a character vector unique by appending sequence numbers to duplicates.

### Usage

    make.unique(names, sep = ".")

### Arguments

`names` | a character vector
`sep` | a character string used to separate a duplicate name from its sequence number.

### Details

The algorithm used by `make.unique` has the property that `make.unique(c(A, B)) == make.unique(c(make.unique(A), B))`.

In other words, you can append one string at a time to a vector, making it unique each time, and get the same result as applying `make.unique` to all of the strings at once.

If character vector `A` is already unique, then `make.unique(c(A, B))` preserves `A`.

### Value

A character vector of same length as `names` with duplicates changed, in the current locale's encoding.

### Author(s)

Thomas P. Minka

### See Also

`make.names`

### Examples

    make.unique(c("a", "a", "a"))
    make.unique(c(make.unique(c("a", "a")), "a"))

    make.unique(c("a", "a", "a.2", "a"))
    make.unique(c(make.unique(c("a", "a")), "a.2", "a"))

    ## Now show a bit where this is used :
    trace(make.unique)
    ## Applied in data.frame() constructions:
    (d1 <- data.frame(x = 1, x = 2, x = 3)) # direct
     d2 <- data.frame(data.frame(x = 1, x = 2), x = 3) # pairwise
    stopifnot(identical(d1, d2),
              colnames(d1) == c("x", "x.1", "x.2"))
    untrace(make.unique)

[Package base version 4.0.5 Index]