The R Project SVN R

% File src/library/base/man/numeric.Rd

% Part of the R package, http://www.R-project.org

% Copyright 1995-2013 R Core Team

% Distributed under GPL 2 or later

\name{numeric}

\title{Numeric Vectors}

\alias{numeric}

\alias{as.numeric}

\alias{is.numeric}

\alias{is.numeric.Date}

\alias{is.numeric.POSIXt}

\description{

  Creates or coerces objects of type \code{"numeric"}.

  \code{is.numeric} is a more general test of an object being

  interpretable as numbers.

}

\usage{

numeric(length = 0)

as.numeric(x, \dots)

is.numeric(x)

}

\arguments{

  \item{length}{A non-negative integer specifying the desired length.

    Double values will be coerced to integer:

    supplying an argument of length other than one is an error.}

  \item{x}{object to be coerced or tested.}

  \item{\dots}{further arguments passed to or from other methods.}

}

\details{

  \code{numeric} is identical to \code{\link{double}} (and \code{real}).

  It creates a double-precision vector of the specified length with each

  element equal to \code{0}.

  \code{as.numeric} is a generic function, but S3 methods must be

  written for \code{\link{as.double}}.  It is identical to \code{as.double}.

  \code{is.numeric} is an \link{internal generic} \code{primitive}

  function: you can write methods to handle specific classes of objects,

  see \link{InternalMethods}.  It is \strong{not} the same as

  \code{\link{is.double}}.  Factors are handled by the default method,

  and there are methods for classes \code{"\link{Date}"},

  \code{"\link{POSIXt}"} and \code{"\link{difftime}"} (all of which

  return false).  Methods for \code{is.numeric} should only return true

  if the base type of the class is \code{double} or \code{integer}

  \emph{and} values can reasonably be regarded as numeric

  (e.g. arithmetic on them makes sense, and comparison should be done

  via the base type).

}

\value{

  for \code{numeric} and \code{as.numeric} see \code{\link{double}}.

  The default method for \code{is.numeric} returns \code{TRUE}

  if its argument is of \link{mode} \code{"numeric"}

  (\link{type} \code{"double"} or type \code{"integer"}) and not a

  factor, and \code{FALSE} otherwise.  That is,

  \code{is.integer(x) || is.double(x)}, or

  \code{(mode(x) == "numeric") && !is.factor(x)}.

}

\section{S4 methods}{

  \code{as.numeric} and \code{is.numeric} are internally S4 generic and

  so methods can be set for them \emph{via} \code{setMethod}.

  To ensure that \code{as.numeric} and \code{as.double}

  remain identical, S4 methods can only be set for \code{as.numeric}.

}

%% keep next the same in double.Rd & numeric.Rd

\section{Note on names}{

  It is a historical anomaly that \R has two names for its

  floating-point vectors, \code{\link{double}} and \code{\link{numeric}}

  (and formerly had \code{real}).

  \code{double} is the name of the \link{type}.

  \code{numeric} is the name of the \link{mode} and also of the implicit

  \link{class}.  As an S4 formal class, use \code{"numeric"}.

  The potential confusion is that \R has used \emph{\link{mode}}

  \code{"numeric"} to mean \sQuote{double or integer}, which conflicts

  with the S4 usage.  Thus \code{is.numeric} tests the mode, not the

  class, but \code{as.numeric} (which is identical to \code{as.double})

  coerces to the class.

}

\seealso{

  \code{\link{double}}, \code{\link{integer}}, \code{\link{storage.mode}}.

}

\references{

  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)

  \emph{The New S Language}.

  Wadsworth & Brooks/Cole.

}

\examples{

as.numeric(c("-.1"," 2.7 ","B")) # (-0.1, 2.7, NA)  +  warning

as.numeric(factor(5:10))

}

\keyword{classes}

\keyword{attribute}