\Header{match.arg}{Argument Verification Using Partial Matching}
\keyword{programming}{match.arg}
\begin{Description}\relax
\code{match.arg} matches \code{arg} against a table of candidate
values as specified by \code{choices}.
\end{Description}
\begin{Usage}
\begin{verbatim}
match.arg(arg, choices)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{arg}] a character string
\item[\code{choices}] a character vector of candidate values
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
In the one-argument form \code{match.arg(arg)}, the choices are
obtained from a default setting for the formal argument \code{arg} of
the function from which \code{match.arg} was called.

Matching is done using \code{\Link{pmatch}}, so \code{arg} may be
abbreviated.
\end{Details}
\begin{Value}
The unabbreviated version of the unique partial match if there is one;
otherwise, an error is signalled.
\end{Value}
\begin{SeeAlso}\relax
\code{\Link{pmatch}},
\code{\Link{match.fun}},
\code{\Link{match.call}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
require(stats)
## Extends the example for 'switch'
center <- function(x, type = c("mean", "median", "trimmed")) {
  type <- match.arg(type)
  switch(type,
         mean = mean(x),
         median = median(x),
         trimmed = mean(x, trim = .1))
}
x <- rcauchy(10)
center(x, "t")       # Works
center(x, "med")     # Works
try(center(x, "m"))  # Error
\end{ExampleCode}
\end{Examples}

