Hi Kieran,

I'm not very familiar with lattice, but here's a workaround that works for
me. Basically, I just created a new data.frame column that was a factor
(combo$zf), and forced its levels to be what you're looking for here.

require(lattice)

x<-c(1,2,3)
y<-c(2,4,6)
z<-c(0.1,0.5,2)
combo<-expand.grid(x,y,z)
combo<-data.frame(combo)
names(combo)<-c("x","y","z")
outcome<-function(l)
{
(l[1]*l[2])/l[3]
}
resp<-apply(combo,1,outcome)

## Create new column and assign levels
combo$zf <- as.factor(combo$z)
levels(combo$zf) <- paste("z=", levels(combo$zf), sep="")

## Now I use the new variable as the conditioning variable in the plot
levelplot(resp~x*y|zf, data=combo
,pretty=TRUE,region=TRUE,contour=FALSE)

In the future, it would help if you could specify the packages you're using,
since I had to do a little research to find where the "levelplot" function
is from.

Hope this helps,
Ethan



On Tue, Jun 7, 2011 at 9:30 AM, kieran martin <kieranjmartin@gmail.com>wrote:

> Hi,
>
> I've been driving myself insane with this problem. I have a trellis plot of
> contours, and I want each level to have something like "z=value" for each
> one. I can get each one to say z, or each one to say the value (by using
> as.factor) but not both. Heres an artificial example to show what I mean
> (as
> my actual data set is much larger!)
>
> x<-c(1,2,3)
> y<-c(2,4,6)
> z<-c(0.1,0.5,2)
> combo<-expand.grid(x,y,z)
> combo<-data.frame(combo)
> names(combo)<-c("x","y","z")
> outcome<-function(l)
> {
> (l[1]*l[2])/l[3]
> }
> resp<-apply(combo,1,outcome)
> levelplot(resp~x*y|z,data=combo
> ,pretty=TRUE,region=TRUE,contour=FALSE)
>
> , so in this final graph I want the z=0.1, z=0.5 and z=2 in turn.
>
> Thanks,
>
> Kieran Martin
> University of Southampton
>
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