qqmath {lattice}R Documentation

Q-Q Plot with Theoretical Distribution

Description

Quantile-Quantile plot of a sample and a theoretical distribution

Usage

qqmath(x, data, ...)

## S3 method for class 'formula':
qqmath(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"),
       ...,
       lattice.options = NULL,
       default.scales = list(),
       subscripts,
       subset)
## S3 method for class 'numeric':
qqmath(x, data = NULL, ylab, ...)

Arguments

x The object on which method dispatch is carried out.
For the "formula" method, a formula of the form ~ x | g1 * g2 * ..., where x must be a numeric. For the "numeric" method, a numeric vector.
data For the formula method, an optional data frame in which variables in the formula (as well as groups and subset, if any) are to be evaluated. Usualll ignored with a warning in other methods.
distribution a quantile function that takes a vector of probabilities as argument and produces the corresponding quantiles. Possible values are qnorm, qunif etc. Distributions with other required arguments need to be passed in as user defined functions.
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 ppoints, which is also the S-PLUS default. If specified, the probabilities generated by this function is used for the plotted quantiles, using the quantile function for the sample, and the function specified as the distribution argument for the theoretical distribution.
f.value defaults to NULL, which has the effect of using ppoints for the quantiles of the theoretical distribution, but the exact data values for the sample. This is similar to what happens for qqnorm, but different from the S-PLUS default of f.value=ppoints.
For large x, this argument can be useful in plotting a smaller set of quantiles, which is usually enough to capture the pattern.
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 panel.qqmath for details.
allow.multiple, outer, auto.key, aspect, prepanel, scales, strip, groups, xlab, xlim, ylab, ylim, drop.unused.levels, lattice.options, default.scales, subscripts, subset See xyplot
... Further arguments. See corresponding entry in xyplot for non-trivial details.

Details

qqmath produces a Q-Q plot of the given sample and a theoretical distribution. The default behaviour of qqmath is different from the corresponding S-PLUS function, but is similar to qqnorm. See the entry for 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 qqmath itself. In fact, both the arguments distribution and 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 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 xyplot, which should be consulted to learn more detailed usage.

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(s)

Deepayan Sarkar Deepayan.Sarkar@R-project.org

See Also

xyplot, panel.qqmath, panel.qqmathline, prepanel.qqmathline, Lattice, 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, ...)
       })

[Package lattice version 0.15-4 Index]