Revision 97b4cfb290dfd3f530ec50b4b7d9545b810a690f authored by Deepayan Sarkar on 11 August 2007, 00:00:00 UTC, committed by Gabor Csardi on 11 August 2007, 00:00:00 UTC
1 parent ef368aa
qqmath.Rd
\name{qqmath}
\alias{qqmath}
\alias{qqmath.formula}
\alias{qqmath.numeric}
\title{ Q-Q Plot with Theoretical Distribution }
\description{
Quantile-Quantile plot of a sample and a theoretical distribution
}
\usage{
qqmath(x, data, \dots)
\method{qqmath}{formula}(x,
data,
allow.multiple = is.null(groups) || outer,
outer = !is.null(groups),
distribution = qnorm,
f.value = NULL,
auto.key = FALSE,
aspect = "fill",
panel = lattice.getOption("panel.qqmath"),
prepanel = NULL,
scales, strip, groups,
xlab, xlim, ylab, ylim,
drop.unused.levels = lattice.getOption("drop.unused.levels"),
\dots,
lattice.options = NULL,
default.scales = list(),
subscripts,
subset)
\method{qqmath}{numeric}(x, data = NULL, ylab, \dots)
}
\arguments{
\item{x}{
The object on which method dispatch is carried out.
For the \code{"formula"} method, a formula of the form \code{~ x |
g1 * g2 * \ldots}, where \code{x} must be a numeric. For the
\code{"numeric"} method, a numeric vector.
}
\item{data}{
For the \code{formula} method, an optional data frame in which
variables in the formula (as well as \code{groups} and
\code{subset}, if any) are to be evaluated. Usualll ignored with a
warning in other methods.
}
\item{distribution}{ a quantile function that takes a vector of
probabilities as argument and produces the corresponding
quantiles. Possible values are \code{qnorm}, \code{qunif} etc.
Distributions with other required arguments need to be passed in as
user defined functions.
}
\item{f.value}{ optional numeric vector of probabilities, quantiles
corresponding to which should be plotted. Can also be a function of
a single integer (representing sample size) that returns such a
numeric vector. The typical value for this argument is the function
\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 for the sample, and
the function specified as the \code{distribution} argument for the
theoretical distribution.
\code{f.value} defaults to \code{NULL}, which has the effect of
using \code{ppoints} for the quantiles of the theoretical
distribution, but the exact data values for the sample. This is
similar to what happens for \code{qqnorm}, but different from the
S-PLUS default of \code{f.value=ppoints}.
For large \code{x}, this argument can be useful in plotting a
smaller set of quantiles, which is usually enough to capture the
pattern.
}
\item{panel}{
The panel function to be used. Unlike in older versions, the
default panel function does most of the actual computations and has
support for grouping. See \code{\link{panel.qqmath}} for details.
}
\item{allow.multiple, outer, auto.key, aspect, prepanel, scales,
strip, groups, xlab, xlim, ylab, ylim, drop.unused.levels,
lattice.options, default.scales, subscripts, subset}{ See
\code{\link{xyplot}} }
\item{\dots}{
Further arguments. See corresponding entry in \code{\link{xyplot}}
for non-trivial details.
}
}
\value{
An object of class \code{"trellis"}. The
\code{\link[lattice:update.trellis]{update}} method can be used to
update components of the object and the
\code{\link[lattice:print.trellis]{print}} method (usually called by
default) will plot it on an appropriate plotting device.
}
\details{
\code{qqmath} produces a Q-Q plot of the given sample and a
theoretical distribution. The default behaviour of \code{qqmath} is
different from the corresponding S-PLUS function, but is similar to
\code{qqnorm}. See the entry for \code{f.value} for specifics.
The implementation details are also different from S-PLUS. In
particular, all the important calculations are done by the panel (and
prepanel function) and not \code{qqmath} itself. In fact, both the
arguments \code{distribution} and \code{f.value} are passed unchanged
to the panel and prepanel function. This allows, among other things,
display of grouped Q-Q plots, which are often useful. See the help
page for \code{\link{panel.qqmath}} for further details.
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.
}
\author{Deepayan Sarkar \email{Deepayan.Sarkar@R-project.org}}
\seealso{\code{\link{xyplot}}, \code{\link{panel.qqmath}},
\code{\link{panel.qqmathline}}, \code{\link{prepanel.qqmathline}},
\code{\link{Lattice}}, \code{\link{quantile}}
}
\examples{
qqmath(~ rnorm(100), distribution = function(p) qt(p, df = 10))
qqmath(~ height | voice.part, aspect = "xy", data = singer,
prepanel = prepanel.qqmathline,
panel = function(x, ...) {
panel.qqmathline(x, ...)
panel.qqmath(x, ...)
})
vp.comb <-
factor(sapply(strsplit(as.character(singer$voice.part), split = " "),
"[", 1),
levels = c("Bass", "Tenor", "Alto", "Soprano"))
vp.group <-
factor(sapply(strsplit(as.character(singer$voice.part), split = " "),
"[", 2))
qqmath(~ height | vp.comb, data = singer,
groups = vp.group, auto.key = list(space = "right"),
aspect = "xy",
prepanel = prepanel.qqmathline,
panel = function(x, ...) {
panel.qqmathline(x, ...)
panel.qqmath(x, ...)
})
}
\keyword{dplot}
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