\name{qq}
\alias{qq}
\title{ Quantile-Quantile Plots of Two Samples }
\description{
Quantile-Quantile plots for comparing two Distributions
}
\synopsis{
qq(formula, data = parent.frame(), aspect = "fill",
panel = panel.qq, prepanel = NULL, scales = list(), strip = TRUE,
groups = NULL, xlab, xlim, ylab, ylim, f.value = NULL,
drop.unused.levels,
..., default.scales,
subscripts = !is.null(groups), subset = TRUE)
}
\usage{
qq(formula, f.value = NULL, ...)
}
\arguments{
\item{formula}{formula of the form \code{y ~ x | g1 * g2 * \ldots},
where \code{x} must be a numeric, and \code{y} can be a factor,
shingle, character or numeric vector, with the restriction that there
must be exactly two levels of \code{y}, which divide the values of
\code{x} into two groups. Quantiles for these groups will be plotted
along the two axes.
}
\item{f.value}{ optional function of a single integer (representing
the larger of the two sample sizes), returning a vector of
probabilities corresponding to which quantiles should be
plotted. The typical value for this argument is \code{ppoints},
which is also the S-PLUS default. If specified, the probabilities
generated by this function is used for the plotted quantiles, using
the \code{quantile} function.
\code{f.value} defaults to \code{NULL}, which is equivalent to
using \code{function(n) ppoints(n, a = 1)}. This has the effect of
including the minimum and maximum data values in the computed
quantiles. This is similar to what happens for \code{qqplot} but
different from the default \code{qq} behaviour in S-PLUS.
}
\item{\dots}{Other arguments}
}
\value{
An object of class ``trellis''. The `update' method can be used to
update components of the object and the `print' method (usually called
by default) will plot it on an appropriate plotting device.
}
\author{Deepayan Sarkar \email{deepayan@stat.wisc.edu}}
\details{
\code{qq} produces a Q-Q plot of two samples. The default behaviour
of \code{qq} is different from the corresponding S-PLUS function. See
the entry for \code{f.value} for specifics.
This 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.
}
\seealso{\code{\link{xyplot}}, \code{\link{panel.qq}},
\code{\link{qqmath}}, \code{\link{Lattice}}
}
\examples{
qq(voice.part ~ height, aspect = 1, data = singer,
subset = (voice.part == "Bass 2" | voice.part == "Tenor 1"))
}
\keyword{dplot}