Create a graphics symbol map that associates data values with graphical symbols.
symbolmap(..., range = NULL, inputs = NULL)An object of class "symbolmap".
Named arguments specifying the graphical parameters. See Details.
Optional. Range of numbers that are mapped.
A numeric vector of length 2 giving the minimum and maximum
values that will be mapped.
Incompatible with inputs.
Optional. A vector containing all the data values
that will be mapped to symbols.
Incompatible with range.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner rolfturner@posteo.net and Ege Rubak rubak@math.aau.dk.
A graphical symbol map is an association between
data values and graphical symbols.
The command symbolmap creates an object of class
"symbolmap" that represents a graphical symbol map.
Once a symbol map has been created, it can be applied to any suitable data to generate a plot of those data. This makes it easy to ensure that the same symbol map is used in two different plots. The symbol map can be plotted as a legend to the plots, and can also be plotted in its own right.
The possible values of data that will be mapped
are specified by range or inputs.
if range is given, it should be a numeric vector
of length 2 giving the minimum and maximum values of the range
of numbers that will be mapped. These limits must be finite.
if inputs is given, it should be a vector
of any atomic type (e.g. numeric, character, logical, factor).
This vector contains all the possible data values
that will be mapped.
If neither range nor inputs is given,
it is assumed that the possible values are real numbers.
The association of data values with graphical symbols
is specified by the other arguments ...
which are given in name=value form.
These arguments specify the kinds of symbols that will be
used, the sizes of the symbols, and graphics parameters for
drawing the symbols.
Each graphics parameter can be either a single
value, for example shape="circles",
or a function(x) which determines the value
of the graphics parameter as a function of the data x,
for example shape=function(x) ifelse(x > 0, "circles", "squares").
Colourmaps (see colourmap) are also acceptable
because they are functions.
Currently recognised graphics parameters, and their allowed values, are:
The shape of the symbol: currently
either "circles", "squares", "arrows",
"crossticks" or NA.
This parameter takes precedence over pch.
(Crossticks are used only for point patterns on a linear network).
The size of the symbol: a positive number or zero.
Graphics character code:
a positive integer, or a single character.
See par.
Graphics character expansion factor.
Colour of plotting characters.
Colour of foreground (or symbol border) and background (or symbol interior).
Colour, width and style of lines.
Logical. If TRUE, each symbol is surrounded
by a border drawn in the opposite colour,
which improves its visibility against the background.
Default is FALSE.
Numeric parameters of arrow symbols, applicable when
shape="arrows". Here direction is the direction
of the arrow in degrees anticlockwise from the \(x\) axis;
headlength is the length of the head of the arrow in
coordinate units; headangle is the angle subtended by the point
of the arrow; and arrowtype is an integer code
specifying which ends of the shaft have arrowheads
attached (0 means no arrowheads, 1 is an arrowhead at the start
of the shaft, 2 is an arrowhead at the end of the shaft, and
3 is arrowheads at both ends).
A vector of colour values is also acceptable for the arguments
col,cols,fg,bg if
range is specified.
plot.symbolmap to plot the symbol map itself.
invoke.symbolmap to apply the symbol map to some data
and plot the resulting symbols.
update.symbolmap to change the symbol map.
There are methods for print and summary for symbol maps.
g <- symbolmap(inputs=letters[1:10], pch=11:20)
g1 <- symbolmap(range=c(0,100), size=function(x) x/50)
g2 <- symbolmap(shape=function(x) ifelse(x > 0, "circles", "squares"),
size=function(x) sqrt(ifelse(x > 0, x/pi, -x)),
bg = function(x) ifelse(abs(x) < 1, "red", "black"))
colmap <- colourmap(topo.colors(20), range=c(0,10))
g3 <- symbolmap(pch=21, bg=colmap, range=c(0,10))
plot(g3)
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