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.
trellis.par.set(name, value, ..., theme, warn = TRUE, strict = FALSE) trellis.par.get(name = NULL)show.settings(x = NULL)
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
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
one for black and white plots (mostly useful for
and one for color printers (color
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
trellis.par.* are meant to be interfaces to the
global settings. They always apply on the settings for the currently
trellis.par.get, called without any arguments, returns the full
list of settings for the active device. With the
present, it returns that component only.
the value of the
name component of the current active device
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"
More convenient (but not S compatible) ways to do this are
trellis.par.set(list(add.line = list(col = "red")))
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.
trellis.par.get returns a list giving parameters for that
name is missing, it returns the full list.
In some ways,
together are a replacement for the
par function used in
traditional R graphics. In particular, changing
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
directly. If the grid package is not attached (lattice itself
only loads the grid namespace), this may be done using