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(),
        subscripts,
        subset)

### Arguments

`x` | The object on which method dispatch is carried out. For the formula method, a formula of the form `y ~ x | g1 * g2 * ...`, where `x` must be a numeric, and `y` can be a factor, shingle, character or numeric vector, 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 along the two axes.
`data` | For the `formula` methods, an optional data frame in which variables in the formula (as well as `groups` and `subset`, if any) are to be evaluated.

`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.
`f.value` defaults to `NULL`, which is equivalent to using `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 `qq` behaviour in S-PLUS.
For large data, this argument can be useful in plotting a smaller set of quantiles, which is usually enough to capture the pattern.

`panel` | The function that uses the packet (subset of display variables) corresponding to a panel to create a display. Default panel functions are documented separately, and often have arguments that can be used to customize its display in various ways. Such arguments can usually be directly supplied to the high level function.
`qtype` | `type` argument for the `quantile`
`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

`qq` produces a Q-Q plot 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 0.17-17 Index]