lattice (version 0.20-45)

# B_05_qq: Quantile-Quantile Plots of Two Samples

## Description

Quantile-Quantile plots for comparing two Distributions

## 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 to

```      f.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.

## 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.

## 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.

`xyplot`, `panel.qq`, `qqmath`, `Lattice`
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