% File src/library/base/man/integer.Rd
% Part of the R package, http://www.R-project.org
% Copyright 1995-2010 R Core Team
% Distributed under GPL 2 or later

\name{integer}
\alias{integer}
\alias{as.integer}
\alias{is.integer}
\title{Integer Vectors}
\description{
  Creates or tests for objects of type \code{"integer"}.
}
\usage{
integer(length = 0)
as.integer(x, \dots)
is.integer(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{
  Integer vectors exist so that data can be passed to C or Fortran code
  which expects them, and so that (small) integer data can be represented
  exactly and compactly.

  Note that current implementations of \R use 32-bit integers for
  integer vectors, so the range of representable integers is restricted
  to about \eqn{\pm 2 \times 10^9}{+/-2*10^9}: \code{\link{double}}s can
  hold much larger integers exactly.
}
\value{
  \code{integer} creates a integer vector of the specified length.
  Each element of the vector is equal to \code{0}.

  \code{as.integer} attempts to coerce its argument to be of integer
  type.  The answer will be \code{NA} unless the coercion succeeds.  Real
  values larger in modulus than the largest integer are coerced to
  \code{NA} (unlike S which gives the most extreme integer of the same
  sign).  Non-integral numeric values are truncated towards zero (i.e.,
  \code{as.integer(x)} equals \code{\link{trunc}(x)} there), and
  imaginary parts of complex numbers are discarded (with a warning).
  Character strings containing optional whitespace followed by either a
  decimal representation or a hexadecimal representation (starting with
  \code{0x} or \code{0X}) can be converted, as well as any allowed by
  the platform for real numbers.  Like \code{\link{as.vector}} it strips
  attributes including names.  (To ensure that an object \code{x} is of
  integer type without stripping attributes, use
  \code{\link{storage.mode}(x) <- "integer"}.)

  \code{is.integer} returns \code{TRUE} or \code{FALSE} depending on
  whether its argument is of integer \link{type} or not, unless it is a
  factor when it returns \code{FALSE}.
}
\note{
  \code{is.integer(x)} does \bold{not} test if \code{x} contains integer
  numbers!  For that, use \code{\link{round}}, as in the function
  \code{is.wholenumber(x)} in the examples.
}
\references{
  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
  \emph{The New S Language}.
  Wadsworth & Brooks/Cole.
}
\seealso{
  \code{\link{numeric}}, \code{\link{storage.mode}}.

  \code{\link{round}} (and \code{ceiling} and \code{floor} on that help
  page) to convert to integral values.
}
\examples{
## as.integer() truncates:
x <- pi * c(-1:1, 10)
as.integer(x)

is.integer(1) # is FALSE !

is.wholenumber <-
    function(x, tol = .Machine$double.eps^0.5)  abs(x - round(x)) < tol
is.wholenumber(1) # is TRUE
(x <- seq(1, 5, by = 0.5) )
is.wholenumber( x ) #-->  TRUE FALSE TRUE ...
}
\keyword{classes}