# coplot: Conditioning Plots

## Description

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

## Usage

 ```1 2 3 4 5 6 7 8 9``` ```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.

## 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`.

## Value

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

## 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.

`pairs`, `panel.smooth`, `points`.
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28``` ```## 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) }) ```