[R] Controlling text and strip arrangement in xyplot

[hadley wickham]

On 6/19/07, Juan Pablo Lewinger <lewinger at usc.edu> wrote:
> I've searched the archives and read the xyplot help but can't figure
> out the 2 lattice questions below?
>
> Consider:
>
> library(lattice)
> DF <- data.frame(x=rnorm(20), y=rnorm(20), g1=rep(letters[1:2], 10),
>                   g2=rep(LETTERS[1:2], each=10),
> g3=rep(rep(letters[3:4],each=5),2))
>
> xyplot(y ~ x | g1 + g2, groups=g3, data=DF)
>
> 1) Is there a way to get one strip per row and column of panels as
> below instead of the default?
>
>
>         _|__a__|__b__|
>          |
>        B
>          |
>         --
>          |
>        A
>          |

Instead of using lattice, you could use ggplot2
(http://had.co.nz/ggplot2), where this is the default:

(p <- qplot(x, y, data=DF, facets = g1 ~ g2))

> 2) How do I control the text of the strips so that for instance
> instead of "a" and "b" it reads"g1=alpha", "g1=beta" where "alpha"
> and "beta" stand for the corresponding greek symbols? (my difficulty
> here is not with the plotmath symbols but with controlling the text
> of the strips directly from the call to xyplot and not by renaming
> the levels of g1)

It's also possible to do this in ggplot, but some bugs currently stop
it from working. It will work in the next version to be released next
week:

p$strip.text <- function(variable, value) {
	greek <- c("A" = "alpha", "B" = "beta")[value]
	makelabel <- function(g) substitute(variable == greek,
list(variable=as.name(variable), greek=as.name(g)))

	lapply(greek, makelabel)
}
p

Hadley