\name{F_1_panel.xyplot}
\alias{panel.xyplot}
\alias{panel.splom}
\alias{panel.qq}
\title{ Default Panel Function for xyplot }
\description{
  This is the default panel function for \code{xyplot}. Also see
  \code{panel.superpose}.  The default panel functions for
  \code{splom} and \code{qq} are essentially the same function.
}
\usage{
panel.xyplot(x, y, type = "p",
             groups = NULL,
             pch, col, col.line, col.symbol,
             font, fontfamily, fontface,
             lty, cex, fill, lwd,
             horizontal = FALSE, \dots,
             grid = FALSE, abline = NULL,
             jitter.x = FALSE, jitter.y = FALSE,
             factor = 0.5, amount = NULL,
             identifier = "xyplot")
panel.splom(\dots, identifier = "splom")
panel.qq(\dots, identifier = "qq")
}
\arguments{
  \item{x,y}{ variables to be plotted in the scatterplot}
  \item{type}{ character vector consisting of one or more of the
    following: \code{"p"}, \code{"l"}, \code{"h"}, \code{"b"},
    \code{"o"}, \code{"s"}, \code{"S"}, \code{"r"}, \code{"a"},
    \code{"g"}, \code{"smooth"}.  If type has more than one element, an
    attempt is made to combine the effect of each of the components.

    The behaviour if any of the first six are included in \code{type} is
    similar to the effect of \code{type} in \code{\link{plot}} (type
    \code{"b"} is actually the same as \code{"o"}).  \code{"r"} adds a
    linear regression line (same as \code{\link{panel.lmline}}, except
    for default graphical parameters), and \code{"smooth"} adds a loess
    fit (same as \code{\link{panel.loess}}).  \code{"g"} adds a
    reference grid using \code{\link{panel.grid}} in the background (but
    using the \code{grid} argument is now the preferred way to do so).
    \code{"a"} has the effect of calling \code{\link{panel.average}},
    which can be useful for creating interaction plots.  The effect of
    several of these specifications depend on the value of
    \code{horizontal}.

    Type \code{"s"} (and \code{"S"}) sorts the values along one of the
    axes (depending on \code{horizontal}); this is unlike the behavior
    in \code{plot}.  For the latter behavior, use \code{type = "s"} with
    \code{panel = panel.points}.

    See \code{example(xyplot)} and \code{demo(lattice)} for examples.
  }
  \item{groups}{ an optional grouping variable.  If present,
    \code{\link{panel.superpose}} will be used instead to display each
    subgroup }
  \item{col, col.line, col.symbol}{
    default colours are obtained from \code{plot.symbol} and
    \code{plot.line} using \code{\link{trellis.par.get}}.
  }
  \item{font, fontface, fontfamily}{
    font used when \code{pch} is a character
  }
  \item{pch, lty, cex, lwd, fill}{
    other graphical parameters.  \code{fill} serves the purpose of
    \code{bg} in \code{\link{points}} for certain values of \code{pch}
  }
  \item{horizontal}{
    A logical flag controlling the orientation for certain
    \code{type}'s, e.g., \code{"h"}, \code{"s"}, ans \code{"S"}.
  }
  \item{\dots}{
    Extra arguments, if any, for \code{panel.xyplot}.  In most cases
    \code{panel.xyplot} ignores these.  For types "r" and "smooth",
    these are passed on to \code{panel.lmline} and \code{panel.loess}
    respectively.
  }
  \item{grid}{
    A logical flag, character string, or list specifying whether and how
    a background grid should be drawn.  This provides the same
    functionality as \code{type="g"}, but is the preferred alternative
    as the effect \code{type="g"} is conceptually different from that of
    other \code{type} values (which are all data-dependent).  Using the
    \code{grid} argument also allows more flexibility.

    Most generally, \code{grid} can be a list of arguments to be
    supplied to \code{\link{panel.grid}}, which is called with those
    arguments.  Three shortcuts are available:
    \describe{
      \item{\code{TRUE}:}{ roughly equivalent to \code{list(h = -1, v = -1)} }
      \item{\code{"h"}:}{ roughly equivalent to \code{list(h = -1, v = 0)} }
      \item{\code{"v"}:}{ roughly equivalent to \code{list(h = 0, v = -1)} }
    }
    No grid is drawn if \code{grid = FALSE}.
  }
  \item{abline}{
    A numeric vector or list, specifying arguments arguments for
    \code{\link{panel.abline}}, which is called with those arguments.
    If specified as a (possibly named) numeric vector, \code{abline} is
    coerced to a list.  This allows arguments of the form \code{abline =
    c(0, 1)}, which adds the diagonal line, or \code{abline = c(h = 0, v
    = 0)}, which adds the x- and y-axes to the plot.  Use the list form
    for finer control; e.g., \code{abline = list(h = 0, v = 0, col =
      "grey")}.

    For more flexibility, use \code{\link{panel.abline}} directly.
  }
  \item{jitter.x, jitter.y}{ logical, whether the data should be
    jittered before being plotted. }
  \item{factor, amount}{ controls amount of jittering. }
  \item{identifier}{
    A character string that is prepended to the names of grobs
    that are created by this panel function.
  }
}



\details{

  Creates scatterplot of \code{x} and \code{y}, with various
  modifications possible via the type argument. \code{panel.qq} draws a
  45 degree line before calling \code{panel.xyplot}.

  Note that most of the arguments controlling the display can be
  supplied directly to the high-level (e.g. \code{\link{xyplot}}) call.

}

\examples{

types.plain <- c("p", "l", "o", "r", "g", "s", "S", "h", "a", "smooth")
types.horiz <- c("s", "S", "h", "a", "smooth")
horiz <- rep(c(FALSE, TRUE), c(length(types.plain), length(types.horiz)))

types <- c(types.plain, types.horiz)

x <- sample(seq(-10, 10, length.out = 15), 30, TRUE)
y <- x + 0.25 * (x + 1)^2 + rnorm(length(x), sd = 5)

xyplot(y ~ x | gl(1, length(types)),
       xlab = "type", 
       ylab = list(c("horizontal=TRUE", "horizontal=FALSE"), y = c(1/6, 4/6)),
       as.table = TRUE, layout = c(5, 3),
       between = list(y = c(0, 1)),
       strip = function(...) {
           panel.fill(trellis.par.get("strip.background")$col[1])
           type <- types[panel.number()]
           grid::grid.text(label = sprintf('"\%s"', type), 
                           x = 0.5, y = 0.5)
           grid::grid.rect()
       },
       scales = list(alternating = c(0, 2), tck = c(0, 0.7), draw = FALSE),
       par.settings = 
       list(layout.widths = list(strip.left = c(1, 0, 0, 0, 0))),
       panel = function(...) {
           type <- types[panel.number()]
           horizontal <- horiz[panel.number()]
           panel.xyplot(..., 
                        type = type,
                        horizontal = horizontal)
       })[rep(1, length(types))]

}


\author{ Deepayan Sarkar \email{Deepayan.Sarkar@R-project.org}}

\seealso{
  \code{\link{panel.superpose}},
  \code{\link{xyplot}},
  \code{\link{splom}}
}
\keyword{dplot}