qqmath {lattice} R Documentation

## Q-Q Plot with Theoretical Distribution

### Description

Quantile-Quantile plot of a sample and a theoretical distribution

### Usage

```qqmath(x, ...)

## S3 method for class 'formula':
qqmath(x,
data = parent.frame(),
allow.multiple = is.null(groups) || outer,
outer = !is.null(groups),
distribution = qnorm,
f.value = NULL,
auto.key = FALSE,
aspect = "fill",
panel = "panel.qqmath",
prepanel = NULL,
scales, strip, groups,
xlab, xlim, ylab, ylim,
drop.unused.levels = lattice.getOption("drop.unused.levels"),
...,
default.scales = list(),
subscripts,
subset)
## S3 method for class 'numeric':
qqmath(x, data, 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. By default, the environment where the function was called from is used. 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, 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

`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 0.12-11 Index]