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\name{numeric}
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\name{numeric}
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\title{Numeric Vectors}
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\title{Numeric Vectors}
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\alias{numeric}
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\alias{numeric}
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\alias{as.numeric}
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\alias{as.numeric}
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\alias{is.numeric}
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\alias{is.numeric}
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\alias{is.numeric.factor}
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\description{
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  Creates or tests for objects of type \code{"numeric"}.
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}
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\usage{
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\usage{
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numeric(length = 0)
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numeric(length = 0)
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as.numeric(x, \dots)
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as.numeric(x, \dots)
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is.numeric(x)
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is.numeric(x)
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}
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}
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\arguments{
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\arguments{
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  \item{length}{desired length.}
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  \item{length}{desired length.}
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  \item{x}{object to be coerced or tested.}
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  \item{x}{object to be coerced or tested.}
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  \item{\dots}{further arguments passed to or from other methods.}
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  \item{\dots}{further arguments passed to or from other methods.}
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}
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}
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\description{
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\details{
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  \code{as.numeric} is a generic function, but methods must be
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  written for \code{\link{as.double}}, which it calls.
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  \code{is.numeric} is generic: you can write methods to handle
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  specific classes of objects, see \link{InternalMethods}.
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  Note that factors are false for \code{is.numeric} since there is a
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  \code{"factor"} method.
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}
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\value{
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  \code{numeric} creates a real vector of the specified length.  The
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  \code{numeric} creates a real vector of the specified length.  The
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  elements of the vector are all equal to \code{0}.
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  elements of the vector are all equal to \code{0}.
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  \code{as.numeric} attempts to coerce its argument to numeric type
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  \code{as.numeric} attempts to coerce its argument to numeric type
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  (either integer or real).
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  (either integer or real).
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  \code{as.numeric} for factors yields the codes underlying the factor
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    levels, not the numeric representation of the labels.
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  \code{is.numeric} returns \code{TRUE} if its argument is of type real
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  \code{is.numeric} returns \code{TRUE} if its argument is of type numeric
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  or type integer and \code{FALSE} otherwise.
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  or type integer and \code{FALSE} otherwise.
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}
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}
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\details{
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  \code{is.numeric} is  generic: you can write methods to handle
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  specific classes of objects, see \link{InternalMethods}.
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  Note that factors are false for \code{is.numeric} but true for
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  \code{\link{is.integer}}.
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}
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\note{
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\note{
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  \emph{\R has no single precision data type.  All real numbers are
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  \emph{\R has no single precision data type.  All real numbers are
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    stored in double precision format}. While \code{as.numeric} is a
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    stored in double precision format}.
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  generic function, user methods must be written for \code{as.double},
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  which it calls
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  \code{as.numeric} for factors yields the codes underlying the factor
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    levels, not the numeric representation of the labels.
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}
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}
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\references{
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\references{
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  \emph{The New S Language}.
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  \emph{The New S Language}.
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  Wadsworth \& Brooks/Cole.
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  Wadsworth \& Brooks/Cole.