The R Project SVN R

\name{exists}
\title{Is an Object Defined?}
\usage{
exists(x, where = -1, envir = parent.frame(),
       frame = NULL, mode = "any", inherits = TRUE)
}
\alias{exists}
\arguments{
  \item{x}{a variable name (given as a character string).}
  \item{where}{where to look for the object (see the details section); if
    omitted, the function will search, as if the name of the object
    appeared in unquoted in an expression.}
  \item{envir}{an alternative way to specify an environment to look in,
    but it's usually simpler to just use the \code{where} argument.}
  \item{frame}{a frame in the calling list.  Equivalent to giving \code{where}
    as \code{sys.frame(frame)}.}
  \item{mode}{the mode of object sought.}
  \item{inherits}{should the enclosing frames of the environment be inspected.}
}
\description{
  Search for an \R object of the given name on the search path.
}
\value{
  Logical, true if and only if the object is found on the search path.
}
\details{
  The \code{where} argument can specify the  environment in which to look
  for the object in any of several ways:
  as an integer (the position in the \code{\link{search}} list); as
  the character string name of an element in the search list; or as an
  \code{\link{environment}} (including using \code{\link{sys.frame}} to
  access the currently active function calls).
  The \code{envir} argument is an alternative way to specify an
  environment, but is primarily there for back compatibility.
  
  This function looks to see if the name \code{x} has a value bound to it.
  If \code{inherits} is \code{TRUE} and a value is not found for \code{x},
  then the parent frames of the environment are searched until the name
  \code{x} is encountered.  \bold{Warning:} This is the default behaviour
  for \R but not for S.

  If \code{mode} is specified then only objects of that mode are sought.
  The function returns \code{TRUE} if the variable is encountered and
  \code{FALSE} if not.

  The \code{mode} includes collections such as \code{"numeric"} and
  \code{"function"}: any member of the collection will suffice.
}
\seealso{
  \code{\link{get}}.
}
\examples{
##  Define a substitute function if necessary:
if(!exists("some.fun", mode="function"))
 some.fun <- function(x) { cat("some.fun(x)\n"); x }
search()
exists("ls", 2) # true even though ls is in pos=3
exists("ls", 2, inherits=FALSE) # false
}
\keyword{data}