% File src/library/base/man/Round.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2021 R Core Team
% Distributed under GPL 2 or later

\name{Round}
\alias{ceiling}
\alias{floor}
\alias{round}
\alias{signif}
\alias{trunc}
\title{Rounding of Numbers}
\usage{
ceiling(x)
floor(x)
trunc(x, \dots)

round(x, digits = 0, \dots)
signif(x, digits = 6)
}
\description{
  \code{ceiling} takes a single numeric argument \code{x} and returns a
  numeric vector containing the smallest integers not less than the
  corresponding elements of \code{x}.

  \code{floor} takes a single numeric argument \code{x} and returns a
  numeric vector containing the largest integers not greater than the
  corresponding elements of \code{x}.

  \code{trunc} takes a single numeric argument \code{x} and returns a
  numeric vector containing the integers formed by truncating the values in
  \code{x} toward \code{0}.

  \code{round} rounds the values in its first argument to the specified
  number of decimal places (default 0).  See \sQuote{Details} about
  \dQuote{round to even} when rounding off a 5.

  \code{signif} rounds the values in its first argument to the specified
  number of \emph{significant} digits.   Hence, for \code{numeric} \code{x},
  \code{signif(x, dig)} is the same as \code{round(x, dig - ceiling(log10(abs(x))))}.
}
\arguments{
  \item{x}{a numeric vector.  Or, for \code{round} and \code{signif}, a
    complex vector.}

  \item{digits}{integer indicating the number of decimal places
    (\code{round}) or significant digits (\code{signif}) to be used.
    For \code{round}, negative values are allowed (see \sQuote{Details}).}

  \item{\dots}{arguments to be passed to methods.}
}
\details{
  These are generic functions: methods can be defined for them
  individually or via the \code{\link[=S3groupGeneric]{Math}} group
  generic.

  Note that for rounding off a 5, the \abbr{IEC} 60559 standard (see also
  \sQuote{IEEE 754}) is expected to be used, \sQuote{\emph{go to the even digit}}.
  Therefore \code{round(0.5)} is \code{0} and \code{round(-1.5)} is
  \code{-2}.  However, this is dependent on OS services and on
  representation error (since e.g.\sspace{}\code{0.15} is not represented
  exactly, the rounding rule applies to the represented number and not
  to the printed number, and so \code{round(0.15, 1)} could be either
  \code{0.1} or \code{0.2}).

  Rounding to a negative number of digits means rounding to a power of
  ten, so for example \code{round(x, digits = -2)} rounds to the nearest
  hundred.

  For \code{signif} the recognized values of \code{digits} are
  \code{1...22}, and non-missing values are rounded to the nearest
  integer in that range. Each element of the vector is rounded individually, 
  unlike printing.

  These are all primitive functions.
}
\section{S4 methods}{
  These are all (internally) S4 generic.

  \code{ceiling}, \code{floor} and \code{trunc} are members of the
  \code{\link[=S4groupGeneric]{Math}} group generic.  As an S4
  generic, \code{trunc} has only one argument.

  \code{round} and \code{signif} are members of the
  \code{\link[=S4groupGeneric]{Math2}} group generic.
}
\section{Warning}{
  The realities of computer arithmetic can cause unexpected results,
  especially with \code{floor} and \code{ceiling}.  For example, we
  \sQuote{know} that \code{floor(log(x, base = 8))} for \code{x = 8} is
  \code{1}, but \code{0} has been seen on an \R platform.  It is
  normally necessary to use a tolerance.

  Rounding to decimal digits in binary arithmetic is non-trivial (when
  \code{digits != 0}) and may be surprising.  Be aware that most decimal
  fractions are \emph{not} exactly representable in binary double precision.
  In \R 4.0.0, the algorithm for \code{round(x, d)}, for \eqn{d > 0}, has
  been improved to \emph{measure} and round \dQuote{to nearest even},
  contrary to earlier versions of \R (or also to \code{\link{sprintf}()}
  or \code{\link{format}()} based rounding).
}
\references{
  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
  \emph{The New S Language}.  Wadsworth & Brooks/Cole.

  The ISO/\abbr{IEC}/IEEE 60559:2011 standard is available for money from
  \url{https://www.iso.org}.

  The IEEE 754:2008 standard is more openly documented, e.g, at
  \url{https://en.wikipedia.org/wiki/IEEE_754}.
}
\seealso{
  \code{\link{as.integer}}.
  Package \CRANpkg{round}'s \code{\link[round]{roundX}()} for several
  versions or implementations of rounding, including some previous and the
  current \R version (as \code{version = "3d.C"}).
}
\examples{
round(.5 + -2:4) # IEEE / IEC rounding: -2  0  0  2  2  4  4
## (this is *good* behaviour -- do *NOT* report it as bug !)

( x1 <- seq(-2, 4, by = .5) )
round(x1) #-- IEEE / IEC rounding !
x1[trunc(x1) != floor(x1)]
x1[round(x1) != floor(x1 + .5)]
(non.int <- ceiling(x1) != floor(x1))

x2 <- pi * 100^(-1:3)
round(x2, 3)
signif(x2, 3)
}
\keyword{arith}
