# B_05_qq

##### Quantile-Quantile Plots of Two Samples

Quantile-Quantile plots for comparing two Distributions

- Keywords
- dplot

##### Usage

`qq(x, data, …)`# S3 method for formula
qq(x, data, aspect = "fill",
panel = lattice.getOption("panel.qq"),
prepanel, scales, strip,
groups, xlab, xlim, ylab, ylim, f.value = NULL,
drop.unused.levels = lattice.getOption("drop.unused.levels"),
…,
lattice.options = NULL,
qtype = 7,
default.scales = list(),
default.prepanel = lattice.getOption("prepanel.default.qq"),
subscripts,
subset)

##### Arguments

- x
The object on which method dispatch is carried out.

For the

`"formula"`

method,`x`

should be a formula of the form`y ~ x | g1 * g2 * …`

, where`x`

should be a numeric variable, and`y`

a factor, shingle, character, or numeric variable, with the restriction that there must be exactly two levels of`y`

, which divide the values of`x`

into two groups. Quantiles for these groups will be plotted against each other along the two axes.- data
For the

`formula`

method, an optional data source (usually a data frame) in which variables are to be evaluated (see`xyplot`

for details).- f.value
An optional numeric vector of probabilities, quantiles corresponding to which should be plotted. This can also be a function of a single integer (representing sample size) that returns such a numeric vector. A 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, through the`quantile`

function.`f.value`

defaults to`NULL`

, which is equivalent tof.value = 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

`qqplot`

but different from the default behaviour of`qq`

in S-PLUS.For large

`x`

, this argument can be used to restrict the number of quantiles plotted.- panel
A function, called once for each panel, that uses the packet (subset of panel variables) corresponding to the panel to create a display. The default panel function

`panel.qq`

is documented separately, and has arguments that can be used to customize its output in various ways. Such arguments can usually be directly supplied to the high-level function.- qtype
The

`type`

argument for`quantile`

.- aspect
See

`xyplot`

.- prepanel
See

`xyplot`

.- scales
See

`xyplot`

.- strip
See

`xyplot`

.- groups
See

`xyplot`

.- xlab, ylab
See

`xyplot`

.- xlim, ylim
See

`xyplot`

.- drop.unused.levels
See

`xyplot`

.- lattice.options
See

`xyplot`

.- default.scales
See

`xyplot`

.- subscripts
See

`xyplot`

.- subset
See

`xyplot`

.- default.prepanel
Fallback prepanel function. See

`xyplot`

.- …
Further arguments. See corresponding entry in

`xyplot`

for non-trivial details.

##### Details

`qq`

produces Q-Q plots of two samples. The default behaviour of
`qq`

is different from the corresponding S-PLUS function. See the
entry for `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 `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.

##### See Also

##### Examples

```
# NOT RUN {
qq(voice.part ~ height, aspect = 1, data = singer,
subset = (voice.part == "Bass 2" | voice.part == "Tenor 1"))
# }
```

*Documentation reproduced from package lattice, version 0.20-40, License: GPL (>= 2)*