[R] Lattice graphics: minor tick marks and panel.axis() question(s)

[Stephen Tucker]

Hello,

I have been a long-time Traditional graphics user and now moving to
try Lattice graphics. At the moment I cannot figure out how to place
minor tick marks in a figure made with Lattice's xyplot(). In
Traditional graphics, after calling plot() I would make two calls to
axis().

>From the manuals and help documentation I learned that 'scales' takes
multiple 'at' arguments only if they apply to each of the different
panels, so I thought to call 'panel.axis' in my panel
function. However I have a few questions regarding this procedure:

1) the placement of the ticks is not where I expect,

2) I cannot seem to get tick marks to point outwards even when I
set the clipping parameter in trellis parameters to "off"

3) (for multiple panels) I cannot figure out how to specify "bottom"
or "top" in each panel such that they appear on the side that the
default routine places major tickmarks

I have included example code at the bottom of this message.  I would
appreciate any help if these issues are intuitively obvious to an
experienced Lattice user. Thank you very much in advance!

Stephen Tucker [using Windows XP and R 2.4.0]

######### Example code #########

#+++++ Define example data +++++
# x = 0.1 to 10 uniformly spaced in lognormal(base10) scale
# y = log10(x) + random noise
# this is repeated for four groups: a,b,c,d
xpoints = c(rep(1:9,times=2)*10^rep(c(-1,0),each=9),10)
df = data.frame(x=rep(xpoints,times=4),
  y = rep(log10(xpoints),times=4)+rep(rnorm(length(xpoints),0,0.2),times=4),
  g = rep(rep(letters[1:4],each=length(xpoints)),times=4))
#+++++

#+++++ Set clipping parameter +++++
clip = trellis.par.get("clip")
clip$panel = "off"
trellis.par.set("clip",clip)
#+++++

#+++++ Define panel function +++++
# plot x,y points
# draw axis
myPanelFunction = function(x,y,...) {
  xpoints = c(rep(1:9,times=2)*10^rep(c(-1,0),each=9),10)  
  panel.xyplot(x,y,...)
  panel.axis("bottom",at=xpoints,labels=FALSE,
             tck=-0.5) #cannot get positive values of tck to work
}
#+++++

#+++++ Call to xyplot() +++++
xyplot(y~x|g,data=df,
       panel = myPanelFunction,
       scales=list(x=list(log=TRUE,at=c(0.1,1,10),
                     labels=parse(text=paste("10^",-1:1)))),
       index.cond=list(c(3,4,1,2)))
#+++++





 
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