[R] Reference Lines Using Grid Graphics

[Pete Brecknock]

Hi 

I would like to be able to add reference lines to a series of plots that are
built using the Grid graphics package. These lines should coincide with tick
marks which are different on each plot.

I can add the lines manually using the grid.lines() function but would like
to understand how to generate them on the fly.

Any help would be gratefully received.

Kind regards

Pete


#######################################################################
# FUNCTION MYPLOT
#######################################################################
myplot=function(i,j){
 pushViewport(viewport(layout.pos.col=i,layout.pos.row=j)) 
 pushViewport(plotViewport(c(3,2,2,3)))

 x <- runif(10)
 y <- (i+j)*runif(10)

 pushViewport(dataViewport(range(x),pretty(y),name="plotRegion"))
 
 grid.points(x, y)
 grid.rect()
 grid.xaxis()
 grid.yaxis(main=FALSE)
  
 # How can I use grid.lines to create reference lines at the tick marks for
each graph?
 # grid.lines(x=0:1,y=0.2) 

 grid.text(paste("Plot ",i," ",j,sep=""), y = unit(1, "npc") + unit(0.5,
"lines"),  gp = gpar(fontsize = 16))
 popViewport()
 popViewport(2)
}
#######################################################################
# END FUNCTION MYPLOT
#######################################################################


grid.newpage()
grid.rect(gp=gpar(fill="white"))
pushViewport(viewport(layout=grid.layout(2, 2)))
myplot(1,1)
myplot(1,2)
myplot(2,1)
myplot(2,2)
popViewport()

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