xyplot and abline

Use panel.superpose into a panel function
Here is some changes in your function that should do the work, 
I haven't tried it but at least it should be closed to it, 
HTH
Vincent

Suggestions
xyplot(fcast$LOGDIFF~fcast$VINTAGE|fcast$REGION,
       groups=fcast$LAG,
       type="b",mfcol=c(3,5),
       panel=function(x,y,...){
		panel.superpose(x,y,...)
		panel.abline(h=0)
	},
       key=list(columns=3, 
         text=list(paste(c("forecast:  ", "",""),
           unique(fcast$LAG), "years")),
       points=Rows(sps,1:3)))

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of John Charles
Considine
Sent: Thursday, September 22, 2005 10:11 AM
To: r-help
Subject: [R] xyplot and abline


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How should I pass abline to this function so that I get a reference line
at h=0 in each panel?

sps <- trellis.par.get("superpose.symbol")
sps$pch <- 1:10
trellis.par.set("superpose.symbol",sps)
xyplot(fcast$LOGDIFF~fcast$VINTAGE|fcast$REGION,
       groups=fcast$LAG,
       panel=panel.superpose,
       type="b",mfcol=c(3,5),
       key=list(columns=3, 
         text=list(paste(c("forecast:  ", "",""),
           unique(fcast$LAG), "years")),
       points=Rows(sps,1:3)))

Cheers,

JC