R: Graphical Parameters for Trellis Displays

C_02_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. Modifications are made to the settings for the currently active device only.

### Usage

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

### Arguments

`name` | A character string giving the name of a component. If unspecified in `trellis.par.get()`, the return value is a named list containing all the current settings (this can be used to get the valid values for `name`).
`value` | a list giving the desired value of the component. Components that are already defined as part of the current settings but are not mentioned in `value` will remain unchanged.
`theme` | a list decribing how to change the settings, similar to what is returned by `trellis.par.get()`. This is purely for convenience, allowing multiple calls to `trellis.par.set` to be condensed into one. The name of each component must be a valid `name` as described above, with the corresponding value a valid `value` as described above. As in `trellis.device`, `theme` can also be a function that produces such a list when called. The function name can be supplied as a quoted string.
`...` | Multiple settings can be specified in `name = value` form. Equivalent to calling with `theme = list(...)`
`warn` | A logical flag, indicating whether a warning should be issued when `trellis.par.get` is called when no graphics device is open.
`strict` | Usually a logical flag, indicating whether the `value` should be interpreted strictly. Usually, assignment of value to the corresponding named component is fuzzy in the sense that sub-components that are absent from `value` but not currently `NULL` are retained. By specifying `strict = TRUE`, such values will be removed. An even stricter interpretation is allowed by specifying `strict` as a numeric value larger than `1`. In that case, top-level components not specified in the call will also be removed. This is primarily for internal use.
`x` | optional list of components that change the settings (any valid value of `theme`). 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, its 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)`

More convenient (but not S compatible) ways to do this are

`trellis.par.set(list(add.line = list(col = "red")))`

and

`trellis.par.set(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 settings.

### Value

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

### Note

In some ways, `trellis.par.get` and `trellis.par.set` together are a replacement for the `par` function used in traditional R graphics. In particular, changing `par` settings has little (if any) effect on lattice output. Since lattice plots are implemented using Grid graphics, its parameter system does have an effect unless overridden by a suitable lattice parameter setting. Such parameters can be specified as part of a lattice theme by including them in the `grid.pars` component (see `gpar` for a list of valid parameter names).

### Author(s)

Deepayan Sarkar Deepayan.Sarkar@R-project.org

### See Also

`trellis.device`, `Lattice`, `gpar`

### Examples

    show.settings()

[Package lattice version 0.20-6 Index]