[S] RE scales in trellis.arg

29 May 1998 08:45:57 -0400

Last time I wrote:

I am quite sure it is in trellis.args in the UNIX version. The
following is part of the code I used that demonstrates how the arg
scale is used. Unfortunately I can not check because I do not have
UNIX any more (How sad!)

Professor Ripley disagreed. I found a copy of the help file I
printed when I had access to an UNIX. I just tried the Windows
version (which i really disparage) and under trallis.arg is the
following (scales is described here):


aspect = "fill",
between = ,
data = ,
key = ,
layout = ,
main = ,
page = ,
panel = panel.trellis.function,
par.strip.text = ,
prepanel = ,
scales = ,
skip = ,
strip = strip.default,
sub = ,
subscripts = ,
subset = ,
xlab = ,
xlim = ,
ylab = ,
ylim = ,

These arguments are common to all Trellis display functions.
See the documentation for any particular function to read about
any special restrictions or default values involving these
The formula argument is typically given positionally, i.e., as the
first argument to the function; all other arguments are given in
name=value form.

aspect aspect ratio control. A numeric value controls each
panel's physical aspect ratio (vertical size/horizontal size). The
character string "xy" causes the 45-degree banking rule to be used
on the x and y data for all panels. The string "fill" (the default)
adjusts the aspect ratio so that the panels fill the page or
screen. Note that the aspect argument is different for the 3D
functions cloud and wireframe; see trellis.3d.args.
between a list with components named x and y, numeric vectors
that specify the space between the columns and rows of the
displayed panels. The units for between are in character heights.

data an optional data frame or list in which to find the
objects mentioned in formula.
formula formula defining the response and the predictors. In
general, its form is:

y _ x | g1 * g2 * ...

however the given variables g1, g2, ... may be omitted. The y
variable is plotted on the y axis and x plotted on the x axis. The
x and y variables are generally numeric and define the data on each
panel The given variables determine how many panels are produced.
Given variables can be either factors or shingles; numeric given
variables are turned into shingles, character variables into
factors. All variables in the formula must of vectors of equal
length. The formula may also contain expressions for the variables,
e.g. sqrt(count) or log(age+1). If a character vector is a given
variable, it is converted to a factor; a numeric given vector is
converted to a shingle. Missing values (NAs) are allowed. Any
points containing missing values will be omitted from the plot.

key a list of arguments to be passed to the key function. If
the list is non-null, a key is placed on each page. If key contains
a component named space, the software will reserve space for the
legend on the appropriate side of the array of panels; values for
space are "top" (default), "bottom", "left", and "right". See
documentation for key for a full description of the other
components of the key= list.
layout numeric vector giving number of panels in columns, rows,
and pages (note particularly the order of these numbers: columns
before rows). By default, the number of columns is determined by
the number of levels in the first given variable; the number of
rows is the number of levels of the second given variable. If there
is one given variable, the default layout vector is c(0,n), where n
is the number of levels of the given vector. Any time the first
value in the layout vector is 0, the second value is used as the
desired number of panels per page and the actual layout is computed
from this, the aspect ratio of the panels and size of labels in
order to maximize the space devoted to displaying the data. The
pages value can be used to plot only a limited number of pages,
where the rows, columns, and given values might imply more. By
default, the pages value is unlimited.

main character string for a main title to be placed at the
top of each page. This may be a list containing a character string
along with graphical parameters to control size (cex), color (col),
and font (font) of the title.
page A function of one argument that is called at the end of
each page drawn by trellis. The argument gives the page number for
this display. The function can display page numbers, add text or
graphics to each page, etc. The default page function does nothing.
panel A function of two arguments, x and y, that draws the
data display in each panel. Prior to calling the panel function,
the x- and y- coordinate system is set up to accommodate the range
of the x and y values in formula and takes into account the
information in the scales argument. If the panel function is
defined with an argument named subscripts, then the panel function
is called with a third (numeric) argument that tells where the x
and y values come from in the entire set of data.

par.strip.text A list giving graphical parameters to be applied
to the text in strip labels. Most important is the cex= parameter,
that not only controls character size, but also adjusts the height
of the strip labels so that the text fits inside.
prepanel optional function that is called prior to
plotting in order to set up appropriate axis scales and aspect
ratios. A prepanel function gets two arguments, x and y, and is
expected to return a list containing one or more of the following
components: xlim, ylim, dx and dy. When axes are set up, they are
guaranteed to include the xlim and ylim values (unless the limits
are overridden by arguments to the high-level routine of the same
names). The dx and dy vectors are used to compute an aspect ratio
by banking to 45-degrees, in conjunction with the aspect="xy"

scales A list that determines how the x- and y-axes (tick marks
and tick labels) are scaled and drawn. The list contains parameters
in name=value form, and may also contain two other lists of the
same type, named x and y. Parameters specified in the x or y
components affect only that axis; those specified at the top level
of scales affect both axes. The most important scales component is
relation, controlling the relationship between axes on various
panels. The default value, relation="same", ensures that the
horizontal or vertical axes on each panel will be identical.
relation="sliced" gives the same number of data units to
corresponding axes on each panel, ensuring that the number of units
per cm. is identical. Using relation="free" results in each panel
having an axis that accommodates just the data in that panel. For
"sliced" and "free", axes will be drawn for each panel, using more
space on the display. The numeric value tick.number controls the
approximate number of tick marks and labels that appear on the
axis. The logical value draw determines whether the axis as a whole
will be drawn. The logical value alternating determines whether
axes alternate from one side of the group of panels to the other.
(Using alternating=FALSE can save space if long tick labels are
used.) For more precise control, alternating can be a vector that
specifies the side of the plot on which each axis is drawn with
1=bottom/left, 2=top/right, 0=do not draw: alternating=TRUE for a
y-axis is identical to alternating=c(1,2). The value limits
specifies limits for the coordinate system; arguments xlim, and
ylim are a shorthand way of specifying the limits value. Other
parameters that are allowed in scales are those appropriate to the
axis function: at, labels (see documentation for axis), as well as
graphical parameters to control the axis rendering (col, cex). This
argument is different for the 3D functions (cloud and wireframe);
see trellis.3d.args.

skip logical vector. This vector is replicated to be as long
as the total number of panels on the pages specified by layout. For
each panel, the corresponding value of skip determines whether
anything will be plotted on the panel. This is useful for leaving
blanks so that the number of plottable panels matches the number of
levels of one or more given variables. By default, all panels are
strip logical flag or a function. If strip is FALSE, no strip
labels are drawn and no room is left for them. If strip is TRUE,
the function strip.default is used to draw strip labels. Otherwise,
the value of strip can be a function that draws strip labels. See
documentation for strip.default for more details.

sub character string for a subtitle, to be placed at the
bottom of each page. This may be a list containing a character
string along with graphical parameters to control size (cex), color
(col), and font (font) of the subtitle.
subscripts logical value; if TRUE, a 3rd argument named
subscripts is passed to the panel function.
subset a subscript vector appropriate for subscripting the x, y
and given vectors. This can be a numeric vector with positive
integers, one with negative integers indicating which observations
should be omitted, or a logical vector.
xlab character string giving a label for the x-axis. By
default, the expression given for x in formula. This may be a list
containing a character string along with graphical parameters to
control size (cex), color (col), and font (font) of the x-label.

xlim numeric vector of length 2 giving minimum and maximum
values for the x-axes.
ylab character string giving a label for the y-axis. By
default, the expression given for y in formula. This may be a list
containing a character string along with graphical parameters to
control size (cex), color (col), and font (font) of the y-label.
ylim numeric vector of length 2 giving minimum and maximum
values for the y-axes.
... other arguments are passed down to the function panel.

Graphical parameters may also be supplied as arguments to this
function (see par). In addition, the high-level graphics arguments
described under par and the arguments to title may be supplied to
this function. Most of these arguments, when specified, affect all
panels in the plot.

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