\HeaderA{splom}{Scatter Plot Matrices}{splom}
\aliasA{parallel}{splom}{parallel}
\methaliasA{parallel.data.frame}{splom}{parallel.data.frame}
\methaliasA{parallel.formula}{splom}{parallel.formula}
\methaliasA{parallel.matrix}{splom}{parallel.matrix}
\methaliasA{splom.data.frame}{splom}{splom.data.frame}
\methaliasA{splom.formula}{splom}{splom.formula}
\methaliasA{splom.matrix}{splom}{splom.matrix}
\keyword{hplot}{splom}
\begin{Description}\relax
Draw Conditional Scatter Plot Matrices and Parallel Coordinate Plots
\end{Description}
\begin{Usage}
\begin{verbatim}
splom(x, data, ...)
parallel(x, data, ...)

## S3 method for class 'formula':
splom(x,
      data,
      auto.key = FALSE,
      aspect = 1,
      between = list(x = 0.5, y = 0.5),
      panel = lattice.getOption("panel.splom"),
      prepanel,
      scales,
      strip,
      groups,
      xlab,
      xlim,
      ylab = NULL,
      ylim,
      superpanel = lattice.getOption("panel.pairs"),
      pscales = 5,
      varnames,
      drop.unused.levels,
      ...,
      lattice.options = NULL,
      default.scales,
      subset = TRUE)
## S3 method for class 'formula':
parallel(x,
         data,
         auto.key = FALSE,
         aspect = "fill",
         between = list(x = 0.5, y = 0.5),
         panel = lattice.getOption("panel.parallel"),
         prepanel,
         scales,
         strip,
         groups,
         xlab = NULL,
         xlim,
         ylab = NULL,
         ylim,
         varnames,
         horizontal.axis = TRUE,
         drop.unused.levels,
         ...,
         lattice.options = NULL,
         default.scales,
         subset = TRUE)

## S3 method for class 'data.frame':
splom(x, data = NULL, ..., groups = NULL, subset = TRUE)
## S3 method for class 'matrix':
splom(x, data = NULL, ..., groups = NULL, subset = TRUE)

## S3 method for class 'matrix':
parallel(x, data = NULL, ..., groups = NULL, subset = TRUE)
## S3 method for class 'data.frame':
parallel(x, data = NULL, ..., groups = NULL, subset = TRUE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] The object on which method dispatch is carried out.

For the \code{"formula"} method, a formula describing the structure
of the plot, which should be of the form \code{\textasciitilde{} x | g1 * g2 *
      ...}, where \code{x} is a data frame or matrix.  Each of
\code{g1,g2,...} must be either factors or shingles. The
conditioning variables \code{g1, g2, ...} may be omitted.

For the \code{data.frame} methods, a data frame.

\item[\code{data}] For the \code{formula} methods, an optional data frame in which
variables in the formula (as well as \code{groups} and
\code{subset}, if any) are to be evaluated.

\item[\code{aspect}] aspect ratio of each panel (and subpanel), square by default for
\code{splom}.

\item[\code{between}] to avoid confusion between panels and subpanels, the default is to
show the panels of a splom plot with space between them.

\item[\code{panel}] Usual interpretation for \code{parallel}, namely the function that
creates the display within each panel. 

For \code{splom}, the terminology is slightly complicated. The role
played by the panel function in most other high-level functions is
played here by the \code{superpanel} function, which is responsible
for the display for each conditional data subset. \code{panel} is
simply an argument to the default \code{superpanel} function
\code{panel.pairs}, and is passed on to it unchanged. It is used
there to create each pairwise display. See \code{\LinkA{panel.pairs}{panel.pairs}}
for more useful options.


\item[\code{superpanel}] function that sets up the splom display, by default as a scatterplot
matrix.

\item[\code{pscales}] a numeric value or a list, meant to be a less functional substitute
for the \code{scales} argument in \code{xyplot} etc. This argument
is passed to the \code{superpanel} function, and is handled by the
default superpanel function \code{panel.pairs}. The help page for
the latter documents this argument in more detail.

\item[\code{varnames}] character vector giving the names of the p variables in x. By
default, the column names of x.

\item[\code{horizontal.axis}] logical indicating whether the parallel axes should
be laid out horizontally (\code{TRUE}) or vertically (\code{FALSE}).

\item[\code{auto.key, prepanel, scales,
strip, groups, xlab, xlim, ylab, ylim, drop.unused.levels,
lattice.options, default.scales, subset}] See \code{\LinkA{xyplot}{xyplot}} 
\item[\code{...}] Further arguments.  See corresponding entry in
\code{\LinkA{xyplot}{xyplot}} for non-trivial details.  
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
\code{splom} produces Scatter Plot Matrices.  The role usually played
by \code{panel} is taken over by \code{superpanel}, which takes a data
frame subset and is responsible for plotting it.  It is called with
the coordinate system set up to have both x- and y-limits from
\code{0.5} to \code{ncol(z) + 0.5}.  The only built-in option
currently available is \code{\LinkA{panel.pairs}{panel.pairs}}, which calls a
further panel function for each pair \code{(i, j)} of variables in
\code{z} inside a rectangle of unit width and height centered at
\code{c(i, j)} (see \code{\LinkA{panel.pairs}{panel.pairs}} for details).

Many of the finer customizations usually done via arguments to high
level function like \code{xyplot} are instead done by
\code{panel.pairs} for \code{splom}. These include control of axis
limits, tick locations and prepanel calcultions. If you are trying to
fine-tune your \code{splom} plot, definitely look at the
\code{\LinkA{panel.pairs}{panel.pairs}} help page. The \code{scales} argument is
usually not very useful in \code{splom}, and trying to change it may
have undesired effects.

\code{\LinkA{parallel}{parallel}} draws Parallel Coordinate Plots. (Difficult to
describe, see example.)

These and all other high level Trellis functions have several
arguments in common. These are extensively documented only in the
help page for \code{xyplot}, which should be consulted to learn more
detailed usage.
\end{Details}
\begin{Value}
An object of class \code{"trellis"}. The
\code{\LinkA{update}{update}} method can be used to
update components of the object and the
\code{\LinkA{print}{print}} method (usually called by
default) will plot it on an appropriate plotting device.
\end{Value}
\begin{Author}\relax
Deepayan Sarkar \email{Deepayan.Sarkar@R-project.org}
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{xyplot}{xyplot}}, \code{\LinkA{Lattice}{Lattice}}, \code{\LinkA{panel.pairs}{panel.pairs},
    \bsl{}code\{\LinkA{panel.pairs}{panel.pairs}\}
  }
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
super.sym <- trellis.par.get("superpose.symbol")
splom(~iris[1:4], groups = Species, data = iris,
      panel = panel.superpose,
      key = list(title = "Three Varieties of Iris",
                 columns = 3, 
                 points = list(pch = super.sym$pch[1:3],
                 col = super.sym$col[1:3]),
                 text = list(c("Setosa", "Versicolor", "Virginica"))))
splom(~iris[1:3]|Species, data = iris, 
      layout=c(2,2), pscales = 0,
      varnames = c("Sepal\nLength", "Sepal\nWidth", "Petal\nLength"),
      page = function(...) {
          ltext(x = seq(.6, .8, len = 4), 
                y = seq(.9, .6, len = 4), 
                lab = c("Three", "Varieties", "of", "Iris"),
                cex = 2)
      })
parallel(~iris[1:4] | Species, iris) 
parallel(~iris[1:4], iris, groups = Species,
         horizontal.axis = FALSE, scales = list(x = list(rot = 90)))
\end{ExampleCode}
\end{Examples}

