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

[Deepayan Sarkar]

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