[R] highlighting subset of point with xyplot (or Hmisc(xYplot))

[Deepayan Sarkar]

On Friday 16 July 2004 16:32, Patrick Lorch wrote:
> Hello all,
> 	I am trying to use xyplot to give a six panel plot and to highlight 
> only points (in any panel) that meet a certain criterion.  With the 
> plot command I would do something like:
> 	plot.default(filein$Site,filein$circ.conc)
> 	points(filein$Site,filein$circ.conc,type="p",
> 		pch=ifelse(filein$p.value<5e-02,19,21))
> I had thought I could just stick in the pch line from above into either 
> xyplot or xYplot with groups set to Site like:
> 	xyplot(circ.conc~Day|Site,data=allsites.byday,groups=Site, 
> pch=ifelse(allsites.byday$p.value<5e-02,19,21))
> This does not produce any highlighting (all symbols come out as open 
> circles (19)).  I have not messed with writing my own panel functions, 
> though I know that is where the solution must lie.  Hopefully someone 
> has an example that is close enough to help me.  I can send an example 
> plot to anyone that wants one.

It's difficult to check without data, but I believe the following would work:

xyplot(circ.conc ~ Day | Site, data=allsites.byday, 
       ## groups=Site, I don't see the point of this
       groups = p.value<5e-02, 
       pch = c(19, 21))

Note that I have removed the original groups variable, because I don't see a 
point in having that (since Site is already used as a conditioning variable). 
If you really need another grouping variable, then this would become slightly 
more complicated. 

Deepayan