B_05_qq {lattice} | R Documentation

## Quantile-Quantile Plots of Two Samples

### Description

Quantile-Quantile plots for comparing two Distributions

### Usage

    qq(x, data, ...)

    ## S3 method for class '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.

### 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.

### Author(s)

Deepayan Sarkar Deepayan.Sarkar@R-project.org

### See Also

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

### Examples

    qq(voice.part ~ height, aspect = 1, data = singer,
       subset = (voice.part == "Bass 2" | voice.part == "Tenor 1"))

[Package lattice version 0.20-6 Index]