\name{G_latticeParseFormula}
\alias{latticeParseFormula}
\title{Parse Trellis formula}
\usage{
latticeParseFormula(model, data, dimension = 2,
subset = TRUE, groups = NULL,
multiple, outer,
subscripts,
drop)
}
\description{
this function is used by high level Lattice functions like
\code{xyplot} to parse the formula argument and evaluate various
components of the data.
}
\arguments{
\item{model}{
the model/formula to be parsed. This can be in either of two
possible forms, one for 2d and one for 3d formulas, determined by
the \code{dimension} argument. The 2d formulas are of the form
\code{y ~ x| g1 * \dots *gn}, and the 3d formulas are of the form
\code{z ~ x * y | g1 * \dots* gn}. In the first form, \code{y} may
be omitted. The conditioning variables \code{g1, \dots,gn} can be
omitted in either case.
}
\item{data}{ the environment/dataset where the variables in the
formula are evaluated.
}
\item{dimension}{ dimension of the model, see above}
\item{subset}{ index for choosing a subset of the data frame }
\item{groups}{ the grouping variable, if present}
\item{multiple, outer}{
logicals, determining how a \sQuote{+} in the y and x components of
the formula are processed. See \code{\link{xyplot}} for details
}
\item{subscripts}{ logical, whether subscripts are to be calculated }
\item{drop}{
logical or list, similar to the \code{drop.unused.levels} argument
in \code{\link{xyplot}}, indicating whether unused levels of
conditioning factors and data variables that are factors are to be
dropped.
}
}
\value{ returns a list with several components, including \code{left,
right, left.name, right.name, condition} for 2-D, and \code{left,
right.x, right.y, left.name, right.x.name, right.y.name, condition}
for 3-D. Other possible components are groups, subscr
}
\seealso{
\code{\link{xyplot}}, \code{\link{Lattice}}
}
\author{Saikat DebRoy, Deepayan Sarkar \email{Deepayan.Sarkar@R-project.org}}
\keyword{utilities}