\Header{make.names}{Make Syntactically Valid Names}
\keyword{character}{make.names}
\begin{Description}\relax
Make syntactically valid names out of character vectors.
\end{Description}
\begin{Usage}
\begin{verbatim}
make.names(names, unique = FALSE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{names}] character vector to be coerced to syntactically valid
names. This is coerced to character if necessary.
\item[\code{unique}] logical; if \code{TRUE}, the resulting elements are
unique.  This may be desired for, e.g., column names.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
A syntactically valid name consists of letters, numbers and the dot or
underline characters and starts with a letter or the dot not followed
by a number.  Names such as \code{".2way"} are not valid, and neither
are the reserved words.

The character \code{"X"} is prepended if necessary.
All invalid characters are translated to \code{"."}.  A missing value
is translated to \code{"NA"}.  Names which match \R{} keywords have a dot
appended to them.  Duplicated values are altered by
\code{\Link{make.unique}}.
\end{Details}
\begin{Value}
A character vector of same length as \code{names} with each changed to
a syntactically valid name.
\end{Value}
\begin{Note}\relax
Prior to version 1.9.0, underscores were not valid in variable names,
and code that relies on them being converted to dots will no longer
work. The simplest workaround is to use \code{gsub("\_", ".", names)}.
\end{Note}
\begin{SeeAlso}\relax
\code{\Link{make.unique}},
\code{\Link{names}},
\code{\Link{character}},
\code{\Link{data.frame}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
make.names(c("a and b", "a-and-b"), unique=TRUE)
# "a.and.b"  "a.and.b.1"

data(state)
state.name[make.names(state.name) != state.name] # those 10 with a space
\end{ExampleCode}
\end{Examples}

