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Lattice- xyplot
Yufeng Lin
Haipeng Yao
How to use xyplot
data = parent.frame(),
panel = if (is.null(groups)) "panel.xyplot" else "panel.superpose",
outer, aspect = "fill",
as.table = FALSE,
between, groups, key,
auto.key = FALSE, legend,
main, page,
par.strip.text, prepanel, scales,
skip, strip = "strip.default",
sub, xlab, xlim, ylab, ylim,
drop.unused.levels, par.settings, perm.cond, index.cond, ..., default.scales,
panel.groups = "panel.xyplot", subscripts, subset)
parameters in the xyplot function:
1. formula:
• The formula is generally of the form y ~ x | g1 * g2 * ...,
• The formula can also be supplied as y ~ x | g1 + g2 + ....
• The formula of the form ~ x | g1 * g2 * ... is also allowed.
• The conditioning variables g1, g2, ... must be either factors or shingles.
• The formula can involve expressions, e.g. sqrt(), log().
• A special case is when the left and/or right sides of the formula (before the
conditioning variables) contain a `+' sign, e.g., y1+y2 ~ x | a*b. This formula would be
taken to mean that the user wants to plot both y1~x | a*b and y2~x | a*b, but with the
y1~x and y2~x superposed in each panel. The two parts would be distinguished by
different graphical parameters.
• To interpret y1 + y2 as a sum, one can either set allow.multiple=FALSE or use
• A variation on this feature is when the outer argument is set to TRUE as well as
allow.multiple. In that case, the plots are not superposed in each panel, but instead
separated into different panels.
• The x and y variables should both be numeric in xyplot, and an attempt is made to
coerce them if not. However, if either is a factor, the levels of that factor are used as
axis labels
parameters in the xyplot function (2)
2. data:
• A data frame containing values for any variables in the formula, as well as groups and
subset if applicable. By default the environment where the function was called from is
3. allow.multiple, outer:
logical flags to control what happens with formulas like y1 + y2 ~ x.
allow.multiple defaults to TRUE whenever it makes sense, and outer
defaults to FALSE except when groups is explicitly specified or grouping
doesn't make sense for the default panel function
parameters in the xyplot function (3)
4. panel:
• Once the subset of rows defined by each unique combination of the levels of the
grouping variables are obtained, the corresponding x and y variables (or other
variables, as appropriate, in the case of other high level functions) are passed on to
be plotted in each panel.
• The actual plotting is done by the function specified by the panel argument.
• The panel function can be a function object or a character string giving the name of a
predefined function.
• Note it is not guaranteed that panel functions will be supplied only numeric vectors for
the x and y arguments; they can be factors as well (but not shingles). Panel functions
need to handle this case, which in most cases can be done by simply coercing them
to numeric.
Technically speaking, panel functions must be written using Grid graphics functions.
However, knowledge of Grid is usually not necessary to construct new custom panel
functions, there are several predefined panel functions which can help; for example,
panel.grid, panel.loess, etc.
• One case where a bit more is required of the panel function is when the groups
argument is not null. In that case, the panel function should also accept arguments
named groups and subscripts An useful panel function predefined for use in such
cases is panel.superpose, which can be combined with different panel.groups
functions determining what is plotted for each group.
• A panel function can have two other optional arguments for convenience, namely
panel.number and panel.counter.
parameters in the xyplot function (3)
• Applies when panel is panel.superpose (which happens by default in these cases if
groups is non-null)
• controls physical aspect ratio of the panels. It can be specified as a ratio (vertical
size/horizontal size) or as a character string.
• logical that controls the order in which panels should be plotted: if FALSE (the default),
panels are drawn left to right, bottom to top (as in a graph); if TRUE, left to right, top
to bottom.
A list with components x and y (both usually 0 by default), numeric vectors specifying
the space between the panels (units are character heights). x and y are repeated to
account for all panels in a page and any extra components are ignored. The result is
used for all pages in a multipage display.
parameters in the xyplot function (4)
• character string or expression (or a ``grob'') for a subtitle to be placed at the bottom of
each page.
10.xlab /(ylab)
character string or expression giving label for the x-axis/y-axis. Defaults to the
expression for x/y in formula. Can be specified as NULL to omit the label altogether.
• Normally a numeric vector of length 2 (possibly a DateTime object) giving minimum
and maximum for the x-axis/y-axis, or, a character vector, expected to denote the
levels of x/y.
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