# trellis.par.get

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##### Graphical Parameters for Trellis Displays

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.

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

One of the uses of par is to set par(ask = TRUE) making R wait for user input before starting a new graphics page. For Grid graphics, this is done using grid.prompt. Lattice has no separate interface for this, and the user must call grid.prompt directly. If the grid package is not attached (lattice itself only loads the grid namespace), this may be done using grid::grid.prompt(TRUE).

trellis.device, Lattice, grid.prompt, gpar

##### Examples
show.settings()
Documentation reproduced from package lattice, version 0.17-10, License: GPL (>= 2)

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