% File src/library/base/man/make.unique.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2019 R Core Team
% Distributed under GPL 2 or later

\name{make.unique}
\alias{make.unique}
\title{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{
  \item{names}{a character vector}
  \item{sep}{a character string used to separate a duplicate name from
    its sequence number.}
}
\value{
  A character vector of same length as \code{names} with duplicates
  changed, in the current locale's encoding.
}
\details{
  The algorithm used by \code{make.unique} has the property that
  \code{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
  \code{make.unique} to all of the strings at once.

  If character vector \code{A} is already unique, then
  \code{make.unique(c(A, B))} preserves \code{A}.
}
\author{Thomas P. Minka}
\seealso{
  \code{\link{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)
}
\keyword{character}