\HeaderA{latticeParseFormula}{Parse Trellis formula}{latticeParseFormula}
\keyword{utilities}{latticeParseFormula}
\begin{Description}\relax
this function is used by high level Lattice functions like
\code{xyplot} to parse the formula argument and evaluate various
components of the data.
\end{Description}
\begin{Usage}
\begin{verbatim}
latticeParseFormula(model, data, dimension = 2,
                    subset = TRUE, groups = NULL,
                    multiple, outer,
                    subscripts,
                    drop)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{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 \textasciitilde{} x| g1 * ... *gn}, and the 3d formulas are of the form
\code{z \textasciitilde{} x * y | g1 * ...* gn}. In the first form, \code{y} may
be omitted. The conditioning variables \code{g1, ...,gn} can be
omitted in either case.

\item[\code{data}] the environment/dataset where the variables in the 
formula are evaluated. By default, the environment where the
function was called from.

\item[\code{dimension}] dimension of the model, see above
\item[\code{subset}] index for choosing a subset of the data frame 
\item[\code{groups}] the grouping variable, if present
\item[\code{multiple, outer}] logicals, determining how a \sQuote{+} in the y and x components of
the formula are processed. See \code{\LinkA{xyplot}{xyplot}} for details

\item[\code{subscripts}] logical, whether subscripts are to be calculated 
\item[\code{drop}] logical or list, similar to the \code{drop.unused.levels} argument
in \code{\LinkA{xyplot}{xyplot}}, indicating whether unused levels of
conditioning factors and data variables that are factors are to be
dropped.

\end{ldescription}
\end{Arguments}
\begin{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
\end{Value}
\begin{Author}\relax
Saikat DebRoy, Deepayan Sarkar \email{Deepayan.Sarkar@R-project.org}
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{xyplot}{xyplot}}, \code{\LinkA{Lattice}{Lattice}}
\end{SeeAlso}

