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% File src/library/base/man/make.unique.Rd
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2019 R Core Team
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% Distributed under GPL 2 or later
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\name{make.unique}
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\alias{make.unique}
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\title{Make Character Strings Unique}
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\description{
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  Makes the elements of a character vector unique by
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  appending sequence numbers to duplicates.
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}
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\usage{
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make.unique(names, sep = ".")
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}
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\arguments{
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  \item{names}{a character vector.}
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  \item{sep}{a character string used to separate a duplicate name from
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    its sequence number.}
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}
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\value{
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  A character vector of same length as \code{names} with duplicates
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  changed, in the current locale's encoding.
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}
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\details{
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  The algorithm used by \code{make.unique} has the property that
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  \code{make.unique(c(A, B)) == make.unique(c(make.unique(A), B))}.
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  In other words, you can append one string at a time to a vector,
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  making it unique each time, and get the same result as applying
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  \code{make.unique} to all of the strings at once.
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  If character vector \code{A} is already unique, then
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  \code{make.unique(c(A, B))} preserves \code{A}.
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}
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\author{Thomas P. Minka}
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\seealso{
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  \code{\link{make.names}}
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}
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\examples{
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make.unique(c("a", "a", "a"))
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make.unique(c(make.unique(c("a", "a")), "a"))
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make.unique(c("a", "a", "a.2", "a"))
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make.unique(c(make.unique(c("a", "a")), "a.2", "a"))
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## Now show a bit where this is used :
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trace(make.unique)
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## Applied in data.frame() constructions:
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(d1 <- data.frame(x = 1, x = 2, x = 3)) # direct
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 d2 <- data.frame(data.frame(x = 1, x = 2), x = 3) # pairwise
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stopifnot(identical(d1, d2),
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          colnames(d1) == c("x", "x.1", "x.2"))
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untrace(make.unique)
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}
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\keyword{character}