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

[Deepayan Sarkar]

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