[R] lattice xscale.components: different ticks on top/bottom axis

[Boris.Vasiliev at forces.gc.ca]

> On Sat, Apr 2, 2011 at 1:29 AM,  <Boris.Vasiliev at forces.gc.ca> wrote:
> >
> >> On Fri, Mar 11, 2011 at 12:28 AM,
> >> <Boris.Vasiliev at forces.gc.ca> wrote:
> >> > Good afternoon,
> >> >
> >> > I am trying to create a plot where the bottom and top 
> >> > axes have the 
> >> > same scale but different tick marks.  I tried user-defined 
> >> > xscale.component function but it does not produce 
> >> > desired results.
> >> > Can anybody suggest where my use of xscale.component function is 
> >> > incorrect?
> >> >
> >> > For example, the code below tries to create a plot where 
> >> > horizontal 
> >> > axes limits are c(0,10), top axis has ticks at odd integers, and 
> >> > bottom axis has ticks at even integers.
> >> >
> >> > library(lattice)
> >> >
> >> > df <- data.frame(x=1:10,y=1:10)
> >> >
> >> > xscale.components.A <- function(...,user.value=NULL) {
> >> >  # get default axes definition list; print user.value
> >> >  ans <- xscale.components.default(...)
> >> >  print(user.value)
> >> >
> >> >  # start with the same definition of bottom and top axes
> >> >  ans$top <- ans$bottom
> >> >
> >> >  # - bottom labels
> >> >  ans$bottom$labels$at <- seq(0,10,by=2)
> >> >  ans$bottom$labels$labels <- paste("B",seq(0,10,by=2),sep="-")
> >> >
> >> >  # - top labels
> >> >  ans$top$labels$at <- seq(1,9,by=2)
> >> >  ans$top$labels$labels <- paste("T",seq(1,9,by=2),sep="-")
> >> >
> >> >  # return axes definition list
> >> >  return(ans)
> >> > }
> >> >
> >> > oltc <- xyplot(y~x,data=df,
> >> >
> >> > scales=list(x=list(limits=c(0,10),at=0:10,alternating=3)),
> >> >               xscale.components=xscale.components.A,
> >> >               user.value=1)
> >> > print(oltc)
> >> >
> >> > The code generates a figure with incorrectly placed 
> >> > bottom and top 
> >> > labels.  Bottom labels "B-0", "B-2", ... are at 0, 1, ... 
> >> > and top labels "T-1", "T-3", ... are at 0, 1, ...  When 
> >> > axis-function runs out of labels, it replaces labels with NA.
> >> >
> >> > It appears that lattice uses top$ticks$at to place labels and 
> >> > top$labels$labels for labels.  Is there a way to override this 
> >> > behaviour (other than to expand the "labels$labels"  vector to 
> >> > be as long as "ticks$at" vector and set necessary elements to "")?
> >>
> >> Well, <top|bottom>$ticks$at is used to place the ticks, and 
> >> $labels$at is used to place the labels. They should 
> >> typically be the 
> >> same, but you have changed one and not the other.
> >> Everything seems to work if you set $ticks$at to the same 
> >> values as $labels$at:
> >>
> >>
> >>     ##  - bottom labels
> >> +   ans$bottom$ticks$at <- seq(0,10,by=2)
> >>     ans$bottom$labels$at <- seq(0,10,by=2)
> >>     ans$bottom$labels$labels <- paste("B",seq(0,10,by=2),sep="-")
> >>
> >>     ##  - top labels
> >> +   ans$top$ticks$at <- seq(1,9,by=2)
> >>     ans$top$labels$at <- seq(1,9,by=2)
> >>     ans$top$labels$labels <- paste("T",seq(1,9,by=2),sep="-")
> >>
> >>
> >> > Also, can user-parameter be passed into xscale.components() 
> >> > function? (For example, locations and labels of ticks on the top 
> >> > axis).  In the  code above, print(user.value) returns NULL even 
> >> > though in the xyplot() call user.value is 1.
> >>
> >> No. Unrecognized arguments are passed to the panel function only, not 
> >> to any other function. However, you can always define an inline
> >> function:
> >>
> >> oltc <- xyplot(y~x,data=df,
> >>                scales=list(x=list(limits=c(0,10), at = 0:10,
> >>                            alternating=3)),
> >>                xscale.components = function(...)
> >>                            xscale.components.A(..., user.value=1))
> >>
> >> Hope that helps (and sorry for the late reply).
> >>
> >> -Deepayan
> >>
> >
> > Deepyan,
> >
> > Thank you very much for your reply.  It makes things a bit clearer.
> >
> > It other words in the list prepared by xscale.components(), vectors 
> > <top|bottom>$ticks$at and <top|bottom>$labels$at must be the same.
> > If only every second tick is to be labelled then every second label 
> > should be set explicitly to empty strings:
> 
> Now when you put it that way, the current behaviour does seem 
> wrong (I didn't read your original post carefully enough). I 
> guess this was one of the not-yet-implemented things 
> mentioned in the Details section of ?xscale.components.default.
> 
> I have added support for different ticks$at and labels$at in 
> the SVN sources in r-forge. You can test it from there (your 
> original code works as expected). I won't make a new release 
> on CRAN until after R
> 2.13 is released (we are almost in code freeze now).
> 
> -Deepayan
> 

Great!
Thank you very much.
Boris.