Aha! Thank you for the more detailed example.
My solution for that situation is an attribute "position" and function
as.position(). I use this in my book
Statistical Analysis and Data Display
Richard M. Heiberger and Burt Holland
The online files for the book are available at
http://springeronline.com/0-387-40270-5
For this example, you need the function as.position() included in this
email.
### example ########
x <- ordered(c(1,2,3,2,4,3,1,2,4,3,2,1,3),
labels=c("small", "medium", "large", "very.large"))
x
attr(x, "position") <- c(1,2,4,8)
x
as.position(x)
y <- rnorm(length(x))
y
xyplot(y ~ x)
source("~/h2/library/code/as.position.s")
xyplot(y ~ as.position(x))
xyplot(y ~ as.position(x),
scale=list(x=list(at=attr(x,"position"), labels=levels(x))))
xyplot(y ~ as.position(x),
scale=list(x=list(at=attr(x,"position"), labels=levels(x))),
xlab="x")
### end example ########
### as.position.s #########
as.position <- function(x) {
if (is.numeric(x))
x
else {
if (!is.factor(x)) stop("x must be either numeric or factor.")
if (!is.null(attr(x, "position")))
x <- attr(x, "position")[x]
else {
lev.x <- levels(x)
if (inherits(x, "ordered")) {
on.exit(options(old.warn))
old.warn <- options(warn=-1)
if (!any(is.na(as.numeric(lev.x))))
x <- as.numeric(lev.x)[x]
else
x <- as.numeric(ordered(lev.x, lev.x))[x]
}
else
x <- as.numeric(x)
}
}
x
}
## tmp <- ordered(c("c","b","f","f","c","b"), c("c","b","f"))
## as.numeric(tmp)
## as.position(tmp)
##
## tmp <- factor(c("c","b","f","f","c","b"))
## as.numeric(tmp)
## as.position(tmp)
##
## tmp <- factor(c(1,3,5,3,5,1))
## as.numeric(tmp)
## as.position(tmp)
##
## tmp <- ordered(c(1,3,5,3,5,1))
## as.numeric(tmp)
## as.position(tmp)
##
## tmp <- c(1,3,5,3,5,1)
## as.numeric(tmp)
## as.position(tmp)
### end as.position.s #########
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