Default axis annotation utilities

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Description

Lattice funtions provide control over how the plot axes are annotated through a common interface. There are two levels of control. The xscale.components and yscale.components arguments can be functions that determine tick mark locations and labels given a packet. For more direct control, the axis argument can be a function that actually draws the axes. The functions documented here are the defaults for these arguments. They can additonally be used as components of user written replacements.

Usage

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xscale.components.default(lim,
                          packet.number = 0,
                          packet.list = NULL,
                          top = TRUE,
                          ...)
yscale.components.default(lim,
                          packet.number = 0,
                          packet.list = NULL,
                          right = TRUE,
                          ...)
axis.default(side = c("top", "bottom", "left", "right"),
             scales, components, as.table,
             labels = c("default", "yes", "no"),
             ticks = c("default", "yes", "no"),
             ..., prefix)

Arguments

lim

the range of the data in that packet (data subset corresponding to a combination of levels of the conditioning variable). The range is not necessarily numeric; e.g. for factors, they could be character vectors representing levels, and for the various date-time representations, they could be vectors of length 2 with the corresponding class.

packet.number

which packet (counted according to the packet order, described in print.trellis) is being processed. In cases where all panels have the same limits, this function is called only once (rather than once for each packet), in which case this argument will have the value 0.

packet.list

list, as long as the number of packets, giving all the actual packets. Specifically, each component is the list of arguments given to the panel function when and if that packet is drawn in a panel. (This has not yet been implemented.)

top, right

the value of the top and right components of the result, as appropriate. See below for interpretation.

side

on which side the axis is to be drawn. The usual partial matching rules apply.

scales

the appropriate component of the scales argument supplied to the high level function, suitably standardized.

components

list, similar to those produced by xscale.components.default and yscale.components.default.

as.table

the as.table argument in the high level function.

labels

whether labels are to be drawn. By default, the rules determined by scales are used.

ticks

whether labels are to be drawn. By default, the rules determined by scales are used.

...

many other arguments may be supplied, and are passed on to other internal functions.

prefix

A character string identifying the plot being drawn (see print.trellis). Used to retrieve location of current panel in the overall layout, so that axes can be drawn appropriately.

Details

These functions are part of a new API introduced in lattice 0.14 to provide the user more control over how axis annotation is done. While the API has been designed in anticipation of use that was previously unsupported, the implementation has initially focused on reproducing existing capabilities, rather than test new features. At the time of writing, several features are unimplemented. If you require them, please contact the maintainer.

Value

xscale.components.default and yscale.components.default return a list of the form suitable as the components argument of axis.default. Valid components in the return value of xscale.components.default are:

num.limit

A numeric limit for the box.

bottom

A list with two elements, ticks and labels. ticks must be a list with components at and tck which give the location and lengths of tick marks. tck can be a vector, and will be recycled to be as long as at. labels must be a list with components at, labels, and check.overlap. at and labels give the location and labels of the tick labels; this is usually the same as the location of the ticks, but is not required to be so. check.overlap is a logical flag indicating whether overlapping of labels should be avoided by omitting some of the labels while rendering.

top

This can be a logical flag; if TRUE, top is treated as being the same as bottom; if FALSE, axis annotation for the top axis is omitted. Alternatively, top can be a list like bottom.

Valid components in the return value of yscale.components.default are left and right. Their interpretations are analogous to (respectively) the bottom and top components described above.

Author(s)

Deepayan Sarkar Deepayan.Sarkar@R-project.org

See Also

Lattice, xyplot, print.trellis

Examples

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str(xscale.components.default(c(0, 1)))

set.seed(36872)
rln <- rlnorm(100)

densityplot(rln, 
            scales = list(x = list(log = 2), alternating = 3),
            xlab = "Simulated lognormal variates",
            xscale.components = function(...) {
                ans <- xscale.components.default(...)
                ans$top <- ans$bottom
                ans$bottom$labels$labels <- parse(text = ans$bottom$labels$labels)
                ans$top$labels$labels <-
                    if (require(MASS))
                        fractions(2^(ans$top$labels$at))
                    else
                        2^(ans$top$labels$at)
                ans
            })


## Direct use of axis to show two temperature scales (Celcius and
## Fahrenheit).  This does not work for multi-row plots, and doesn't
## do automatic allocation of space


F2C <- function(f) 5 * (f - 32) / 9 
C2F <- function(c) 32 + 9 * c / 5 

axis.CF <-
    function(side, ...) 
{
    ylim <- current.panel.limits()$ylim
    switch(side,
           left = {
               prettyF <- pretty(ylim)
               labF <- parse(text = sprintf("%s ~ degree * F", prettyF))
               panel.axis(side = side, outside = TRUE,
                          at = prettyF, labels = labF)
           },
           right = {
               prettyC <- pretty(F2C(ylim))
               labC <- parse(text = sprintf("%s ~ degree * C", prettyC))
               panel.axis(side = side, outside = TRUE,
                          at = C2F(prettyC), labels = labC)
           },
           axis.default(side = side, ...))
}

xyplot(nhtemp ~ time(nhtemp), aspect = "xy", type = "o",
       scales = list(y = list(alternating = 3)),
       axis = axis.CF, xlab = "Year", ylab = "Temperature", 
       main = "Yearly temperature in New Haven, CT")

## version using yscale.components

yscale.components.CF <-
    function(...)
{
    ans <- yscale.components.default(...)
    ans$right <- ans$left
    ans$left$labels$labels <-
        parse(text = sprintf("%s ~ degree * F", ans$left$labels$at))
    prettyC <- pretty(F2C(ans$num.limit))
    ans$right$ticks$at <- C2F(prettyC)
    ans$right$labels$at <- C2F(prettyC)
    ans$right$labels$labels <-
        parse(text = sprintf("%s ~ degree * C", prettyC))
    ans
}
      

xyplot(nhtemp ~ time(nhtemp), aspect = "xy", type = "o",
       scales = list(y = list(alternating = 3)),
       yscale.components = yscale.components.CF,
       xlab = "Year", ylab = "Temperature", 
       main = "Yearly temperature in New Haven, CT")

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