\HeaderA{update}{Update and Re-fit a Model Call}{update}
\methaliasA{update.default}{update}{update.default}
\keyword{models}{update}
\begin{Description}\relax
\code{update} will update and (by default) re-fit a model. It does this
by extracting the call stored in the object, updating the call and (by
default) evaluating that call. Sometimes it is useful to call
\code{update} with only one argument, for example if the data frame has
been corrected.
\end{Description}
\begin{Usage}
\begin{verbatim}
update(object, ...)

## Default S3 method:
update(object, formula., ..., evaluate = TRUE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{object}] An existing fit from a model function such as \code{lm},
\code{glm} and many others.
\item[\code{formula.}] Changes to the formula -- see \code{update.formula} for
details.
\item[\code{...}] Additional arguments to the call, or arguments with
changed values. Use \code{name=NULL} to remove the argument \code{name}.
\item[\code{evaluate}] If true evaluate the new call else return the call.
\end{ldescription}
\end{Arguments}
\begin{Value}
If \code{evaluate = TRUE} the fitted object, otherwise the updated call.
\end{Value}
\begin{References}\relax
Chambers, J. M. (1992)
\emph{Linear models.}
Chapter 4 of \emph{Statistical Models in S}
eds J. M. Chambers and T. J. Hastie, Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{update.formula}{update.formula}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
oldcon <- options(contrasts = c("contr.treatment", "contr.poly"))
## Annette Dobson (1990) "An Introduction to Generalized Linear Models".
## Page 9: Plant Weight Data.
ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
group <- gl(2, 10, 20, labels = c("Ctl", "Trt"))
weight <- c(ctl, trt)
lm.D9 <- lm(weight ~ group)
lm.D9
summary(lm.D90 <- update(lm.D9, . ~ . - 1))
options(contrasts = c("contr.helmert", "contr.poly"))
update(lm.D9)
options(oldcon)
\end{ExampleCode}
\end{Examples}

