[R] adding a line across plots in xy plot with panel.abline

[Christine Lee]

Dear all,

I want to draw a line at DI=1 across all four graphs in the xy plot, I have used panel.abline, but I failed to do so, does any one has an idea of what has went wrong?

structure(list(Date = structure(c(6L, 7L, 2L, 4L, 13L, 17L, 5L, 
12L, 4L, 11L, 14L, 9L, 7L, 2L, 4L, 13L, 10L, 17L, 5L, 12L, 8L, 
4L, 11L, 14L, 9L, 16L, 15L, 3L, 10L, 1L, 17L, 5L, 12L, 8L, 4L, 
11L, 14L, 12L, 8L, 4L, 11L, 14L), .Label = c("1/10", "1/11", 
"11/11", "12/11", "13/10", "19/9", "2/10", "2/11", "20/9", "23/9", 
"26/11", "29/10", "29/11", "30/11", "31/10", "4/10", "6/10"), class = "factor"), 
    Year = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 
    2L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 
    1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
    2L, 2L), .Label = c("Y2002", "Y2014"), class = "factor"), 
    Station = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
    1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 4L, 4L, 
    4L, 4L, 4L), .Label = c("E", "F", "H", "I"), class = "factor"), 
    DI = c(13.4, 7, 12.6, 12.6, 5.2, 2.2, 1, 1, 1.2, 0.8, 2.3, 
    3.8, 5.4, 4.6, 5, 3.2, 3.1, 8.7, 2.1, 2.7, 4.9, 4, 2.2, 5.3, 
    5.6, 4.8, 4, 8.6, 1.9, 2.9, 5.9, 2.6, 8.9, 4, 13.5, 15.3, 
    12.8, 3.4, 4.7, 1.7, 0.9, 1.7), Date1 = structure(c(16697, 
    16710, 16740, 16751, 16768, 16714, 16721, 16737, 16751, 16765, 
    16769, 16698, 16710, 16740, 16751, 16768, 16701, 16714, 16721, 
    16737, 16741, 16751, 16765, 16769, 16698, 16712, 16739, 16750, 
    16701, 16709, 16714, 16721, 16737, 16741, 16751, 16765, 16769, 
    16737, 16741, 16751, 16765, 16769), class = "Date")), .Names = c("Date", 
"Year", "Station", "DI", "Date1"), row.names = c(NA, -42L), class = "data.frame")
Raw$Date1<-as.Date(Raw$Date,"%d/%m")
culr<-ifelse(Raw$Year=="Y2002","Year 2002","Year 2014")
library(lattice)
xyplot(DI~Date1|Station, data=Raw,
        groups = culr,
        par.settings = list(strip.background = list(col = "transparent"),
                            superpose.symbol = list(cex = rep(2, 2),
                                                    col=c("grey","black"),
                                                    pch = rep(16,2))),
        type="p",
        xlab=list("Month",cex=1.5),
        ylab=list("Dispersion index",cex=1.5),  
        index.cond=list(c(1,2,3,4)),
        auto.key = T,
        layout=c(4,1),
        panel=function(Date1,DI){
        panel.labline(h=1,lty=2,lwd=3)
        })

Many thanks.

Regards,
Christine