The R Project SVN R

\name{expand.model.frame}
\alias{expand.model.frame}
%- Also NEED an `\alias' for EACH other topic documented here.
\title{Add new variables to a model frame}
\description{
Evaluates new variables as if they had been part of the formula of the
specified model.  This ensures that the same \code{na.action} and
\code{subset} arguments are applied and allows eg \code{x} to be
recovered for a model using \code{sin(x)} as a predictor.
}
\usage{
expand.model.frame(model, extras, enclos=sys.frame(sys.parent()), na.expand=FALSE)
}
%- maybe also `usage' for other objects documented here.
\arguments{
 \item{model}{A fitted model}
 \item{extras}{One-sided formula or vector of character strings
   describing new variables to be added}
 \item{enclos}{An environment to evaluate things in}
 \item{na.expand}{See below}
}
\details{
If \code{na.expand=FALSE} then \code{NA} values in the extra variables
will be passed to the \code{na.action} function used in
\code{model}. This may result in a shorter data frame (with
\code{\link{na.omit}}) or an error (with \code{\link{na.fail}}).  If
\code{na.expand=TRUE} the returned data frame will have precisely the
same rows as \code{model.frame(model)}, but the columns corresponding to
the extra variables may contain \code{NA}.
}
\value{
A data frame
}

\seealso{\code{\link{model.frame}},\code{\link{predict}}}

\examples{
data(trees)
model<-lm(log(Volume)~log(Girth)+log(Height),data=trees)
expand.model.frame(model,~Girth)
dd<-data.frame(x=1:5,y=rnorm(5),z=c(1,2,NA,4,5))
model<-glm(y~x,data=dd,subset=1:4,na.action=na.omit)
expand.model.frame(model,"z",na.expand=FALSE)
expand.model.frame(model,"z",na.expand=TRUE)
}
\keyword{manip}%-- one or more ...
\keyword{regression}%-- one or more ...