Hi,

I am having an issue with a custom panel for lattice.  The problem  
comes when I try passing a groups argument.

Here is the custom panel, a wrapper for smooth spline.  I copied  
panel.loess and replaced the loess arguments with smooth.spline().  
[Note: I would like to use the cross-validation fitting properties of  
smooth.spline.]

library(lattice)

panel.smooth.spline<-function(x,y,w=NULL, df, spar = NULL, cv = FALSE,
	lwd=plot.line$lwd, lty=plot.line$lty,col, col.line=plot.line$col,
	type, horizontal=FALSE,... ){
		
	    x <- as.numeric(x)
	    y <- as.numeric(y)
	    ok <- is.finite(x) & is.finite(y)
	    if (sum(ok) < 1)
	        return()
	    if (!missing(col)) {
	        if (missing(col.line))
	            col.line <- col
	    }
	    plot.line <- trellis.par.get("plot.line")
	    if (horizontal) {
	        spline <- smooth.spline(y[ok], x[ok], ...)
	        panel.lines(x = spline$y, y = spline$x, col = col.line,
	            lty = lty, lwd = lwd, ...)
	    }
	    else {
	        spline <- smooth.spline(x[ok], y[ok],...)
	        panel.lines(x = spline$x, y = spline$y, col = col.line,
	            lty = lty, lwd = lwd, ...)
	    }
	}
	

# Here is my test data frame	
set.seed(25)
test<-data.frame(x=c(1:200), y=rnorm(200), groups=gl(4,200/4))

# This call to xyplot works, but the smoother colors are not unique.

xyplot(y~x|groups, data=test,
	panel=function(...){
		panel.xyplot(...)
		panel.smooth.spline(...)
		})

# This call to xyplot doesn't work and results in an error "error  
using packet"

xyplot(y~x|groups, data=test, groups=groups,
	panel=function(...){
		panel.xyplot(...)
		panel.smooth.spline(...)
		})

I think this should be quite simple but I must be too simple minded.
Thanks for any help.

Jon Loehrke
Graduate Research Assistant
Department of Fisheries Oceanography
School for Marine Science and Technology
University of Massachusetts
200 Mill Road, Suite 325
Fairhaven, MA 02719
jloehrke@umassd.edu

sessionInfo()
R version 2.8.0 Patched (2008-11-24 r47017)
i386-apple-darwin9.5.0

locale:
en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] lattice_0.17-17 zoo_1.5-4

loaded via a namespace (and not attached):
[1] grid_2.8.0  tools_2.8.0


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