R: Graphical Parameters for Trellis Displays

trellis.par.get {lattice} | R Documentation

## Graphical Parameters for Trellis Displays

### Description

Functions used to query, display and modify graphical parameters for fine control of Trellis displays.

### Usage

    trellis.par.get(name = NULL)
    trellis.par.set(name, value, warn)
    show.settings(x = NULL)

### Arguments

`name` | character giving the name of a component. For a list of valid values type `names(trellis.par.get())`.
`value` | a list giving the desired value of the component.
`warn` | logical, whether a warning should be issued when `trellis.par.get` is called when no graphics device is open
`x` | optional list of components that change the settings (any valid value of `theme` in `lset`). These are used to modify the current settings (obtained by `trellis.par.get`) before they are displayed

### Details

The various graphical parameters (color, line type, background etc) that control the look and feel of Trellis displays are highly customizable. Also, R can produce graphics on a number of devices, and it is expected that a different set of parameters would be more suited to different devices. These parameters are stored internally in a variable named `lattice.theme`, which is a list whose components define settings for particular devices. The components are idenified by the name of the device they represent (as obtained by `.Device`), and are created as and when new devices are opened for the first time using `trellis.device` (or Lattice plots are drawn on a device for the first time in that session).

The initial settings for each device defaults to values appropriate for that device. In practice, this boils down to three distinct settings, one for screen devices like `x11` and `windows`, one for black and white plots (mostly useful for `postscript`) and one for color printers (color `postcript, pdf`).

Once a device is open, it's settings can be modified. When another instance of the same device is opened later using `trellis.device`, the settings for that device are reset to its defaults, unless otherwise specified in the call to `trellis.device`. But settings for different devices are treated separately, i.e., opening a postscript device will not alter the x11 settings, which will remain in effect whenever an x11 device is active.

The functions `trellis.par.*` are meant to be interfaces to the global settings. They always apply on the settings for the currently ACTIVE device.

`trellis.par.get`, called without any arguments, returns the full list of settings for the active device. With the `name` argument present, it returns that component only. `trellis.par.get` sets the value of the `name` component of the current active device settings to `value`.

`trellis.par.get` is usually used inside trellis functions to get graphical parameters before plotting. Modifications by users via `trellis.par.set` is traditionally done as follows:

`add.line <- trellis.par.get("add.line")`

`add.line$col <- "red"`

`trellis.par.set("add.line", add.line)`

`lset` is a usually more convenient interface to achieve the same end (but is not compatible with S-PLUS), the equivalent usage being:

`lset(list(add.line = list(col = "red")))`

The actual list of the components in `trellis.settings` has not been finalized, so I'm not attempting to list them here. The current value can be obtained by `print(trellis.par.get())`. Most names should be self-explanatory.

`show.settings` provides a graphical display summarizing some of the values in the current setting.

### Value

`trellis.par.get` returns a list giving parameters for that component. If `name` is missing, it returns the full list.

### Author(s)

Deepayan Sarkar deepayan@stat.wisc.edu

### See Also

There are some simpler alternatives that can be used to manipulate the settings. Details can be found in the documentation for `lset`. Other related pages: `trellis.device`, `trellis.par.get`,`Lattice`

### Examples

    show.settings()

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