graphics (version 3.4.0)

coplot: Conditioning Plots

Description

This function produces two variants of the conditioning plots discussed in the reference below.

Usage

coplot(formula, data, given.values, panel = points, rows, columns,
       show.given = TRUE, col = par("fg"), pch = par("pch"),
       bar.bg = c(num = gray(0.8), fac = gray(0.95)),
       xlab = c(x.name, paste("Given :", a.name)),
       ylab = c(y.name, paste("Given :", b.name)),
       subscripts = FALSE,
       axlabels = function(f) abbreviate(levels(f)),
       number = 6, overlap = 0.5, xlim, ylim, …)
co.intervals(x, number = 6, overlap = 0.5)

Arguments

formula

a formula describing the form of conditioning plot. A formula of the form y ~ x | a indicates that plots of y versus x should be produced conditional on the variable a. A formula of the form y ~ x| a * b indicates that plots of y versus x should be produced conditional on the two variables a and b.

All three or four variables may be either numeric or factors. When x or y are factors, the result is almost as if as.numeric() was applied, whereas for factor a or b, the conditioning (and its graphics if show.given is true) are adapted.

data

a data frame containing values for any variables in the formula. By default the environment where coplot was called from is used.

given.values

a value or list of two values which determine how the conditioning on a and b is to take place.

When there is no b (i.e., conditioning only on a), usually this is a matrix with two columns each row of which gives an interval, to be conditioned on, but is can also be a single vector of numbers or a set of factor levels (if the variable being conditioned on is a factor). In this case (no b), the result of co.intervals can be used directly as given.values argument.

panel

a function(x, y, col, pch, …) which gives the action to be carried out in each panel of the display. The default is points.

rows

the panels of the plot are laid out in a rows by columns array. rows gives the number of rows in the array.

columns

the number of columns in the panel layout array.

show.given

logical (possibly of length 2 for 2 conditioning variables): should conditioning plots be shown for the corresponding conditioning variables (default TRUE).

col

a vector of colors to be used to plot the points. If too short, the values are recycled.

pch

a vector of plotting symbols or characters. If too short, the values are recycled.

bar.bg

a named vector with components "num" and "fac" giving the background colors for the (shingle) bars, for numeric and factor conditioning variables respectively.

xlab

character; labels to use for the x axis and the first conditioning variable. If only one label is given, it is used for the x axis and the default label is used for the conditioning variable.

ylab

character; labels to use for the y axis and any second conditioning variable.

subscripts

logical: if true the panel function is given an additional (third) argument subscripts giving the subscripts of the data passed to that panel.

axlabels

function for creating axis (tick) labels when x or y are factors.

number

integer; the number of conditioning intervals, for a and b, possibly of length 2. It is only used if the corresponding conditioning variable is not a factor.

overlap

numeric < 1; the fraction of overlap of the conditioning variables, possibly of length 2 for x and y direction. When overlap < 0, there will be gaps between the data slices.

xlim

the range for the x axis.

ylim

the range for the y axis.

…

additional arguments to the panel function.

x

a numeric vector.

Value

co.intervals(., number, .) returns a (number \(\times\) 2) matrix, say ci, where ci[k,] is the range of x values for the k-th interval.

Details

In the case of a single conditioning variable a, when both rows and columns are unspecified, a ‘close to square’ layout is chosen with columns >= rows.

In the case of multiple rows, the order of the panel plots is from the bottom and from the left (corresponding to increasing a, typically).

A panel function should not attempt to start a new plot, but just plot within a given coordinate system: thus plot and boxplot are not panel functions.

The rendering of arguments xlab and ylab is not controlled by par arguments cex.lab and font.lab even though they are plotted by mtext rather than title.

References

Chambers, J. M. (1992) Data for models. Chapter 3 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.

Cleveland, W. S. (1993) Visualizing Data. New Jersey: Summit Press.

See Also

pairs, panel.smooth, points.

Examples

## Tonga Trench Earthquakes
coplot(lat ~ long | depth, data = quakes)
given.depth <- co.intervals(quakes$depth, number = 4, overlap = .1)
coplot(lat ~ long | depth, data = quakes, given.v = given.depth, rows = 1)

## Conditioning on 2 variables:
ll.dm <- lat ~ long | depth * mag
coplot(ll.dm, data = quakes)
coplot(ll.dm, data = quakes, number = c(4, 7), show.given = c(TRUE, FALSE))
coplot(ll.dm, data = quakes, number = c(3, 7),
       overlap = c(-.5, .1)) # negative overlap DROPS values

## given two factors
Index <- seq(length = nrow(warpbreaks)) # to get nicer default labels
coplot(breaks ~ Index | wool * tension, data = warpbreaks,
       show.given = 0:1)
coplot(breaks ~ Index | wool * tension, data = warpbreaks,
       col = "red", bg = "pink", pch = 21,
       bar.bg = c(fac = "light blue"))

## Example with empty panels:
with(data.frame(state.x77), {
coplot(Life.Exp ~ Income | Illiteracy * state.region, number = 3,
       panel = function(x, y, ...) panel.smooth(x, y, span = .8, ...))
## y ~ factor -- not really sensible, but 'show off':
coplot(Life.Exp ~ state.region | Income * state.division,
       panel = panel.smooth)
})