R help - Jul 2012 - minor axis ticks in trellis graphics?

Dear R users,

I need to add minor axis ticks to my graph. In traditional R this is easily
achievable by simply
adding a second axis with the minor ticks. But how to do that in trellis? I am
already out of ideas.

Any suggestions will be appreciated.

Best regards,

Martin

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On 2012-07-13 01:05, Martin Ivanov wrote:
>   Dear R users,
>
> I need to add minor axis ticks to my graph. In traditional R this is easily
achievable by simply
> adding a second axis with the minor ticks. But how to do that in trellis? I
am already out of ideas.
>
> Any suggestions will be appreciated.
Haven't seen a response yet, so I'll give it a shot,
sure to be replaced by something much simpler by
Deepayan when he finds the time.

Here are two ways:

1.
Assign appropriate values to the elements of
the xscale.components list. I prefer this.

## make some data
d <- data.frame(x = 1:12, y = rnorm(12))
at.ticks <- c(4,8)
at.labels <- c(2,6,10)
the_labels <- letters[1:3]

library(lattice)

## define a function to modify the xscale components;
## this function will be used inside xyplot().
myxscale.components <- function(...)
{
     ans <- xscale.components.default(...)
     ans$bottom$ticks$at <- at.ticks
     ans$bottom$labels$at <- at.labels
     ans$bottom$labels$labels <- the_labels
     ans
}

## do the plot
xyplot(y ~ x, data = d,
     scales = list(tck = c(1,0)),
     xscale.components = myxscale.components)

You can put the modifying function inside the xyplot call.
See ?axis.components.


2.
This is more like the base graphics way.
We create the plot without the x-axis and then
use the trellis.focus/unfocus functions in
conjunction with the panel.axis() function.
See ?panel.axis for details.

Here's the function to apply after the xyplot call:

myfocus <- function(){
   trellis.focus("panel", 1, 1,
      clip.off = TRUE,
      highlight = FALSE)

   ## put the ticks in
   panel.axis(side = "bottom",
      at = at.ticks,
      labels = FALSE,
      ticks = TRUE,
      tck = 1, outside = TRUE
   )

   ## put the labels in
   panel.axis(side = "bottom",
      at = at.labels,
      labels = the_labels,
      ticks = FALSE,
      tck = 0, outside = TRUE,
      rot = 0   # optional; try it without
   )
   trellis.unfocus()
}


xyplot(y ~ x, data = d,
     scales = list(
          y = list(tck = c(1,0)),
          x = list(tck = c(0,0),
                 at = 1, label = ""  # to give us some bottom space
              )))

## Now add the axis ticks and labels
myfocus()


Peter Ehlers

>
> Best regards,
>
> Martin

Dear Martin,

Mea culpa! I screwed up. I was answering (not well, at that) a
different question and somehow managed to make it a response to
your request.

Here's what may be a solution to your problem.
(see also this post by ilai:
<<https://stat.ethz.ch/pipermail/r-help/attachments/20120718/7133b673/attachment.pl>>)

We define appropriate locations for the x-ticks to go with
suitably defined labels and corresponding tick lengths.

## data:
    d <- data.frame(x = 1:11, y = rnorm(11))

## Where to put ticks and labels
    myat  <- 1:11
    mylab <- head(c(rbind(LETTERS[1:6], "")), -1)
       # putting letters at every second tick

## lengths of ticks
    mytck <- head(c(rbind(rep(1,6), .5)), -1)

## myat, mylab, mytck should all be same length

## plot
    xyplot(y ~ x, data = d, xlab="",
      scales = list(x = list(
                 at = myat, labels = mylab)),
      par.settings = list(
                 axis.components = list(
                    bottom = list(tck = mytck))))

## Try it with different myat etc to see how it works

    myat  <- seq(1, 11, by = 2/3)
    mylab <- head(c(rbind(LETTERS[1:6], "", "")), -2)
    mytck <- head(c(rbind(rep(2,6), .5, .5)), -2)

    myat  <- seq(1, 11, by = 1/2)
    mylab <- head(c(rbind(LETTERS[1:6], "", "",
"")), -3)
    mytck <- head(c(rbind(rep(2,6), .5, 1, .5)), -3)

The trick is in constructing suitable vectors myat, mylab,
and mytck which you can do any way you like but I would
check that the lengths are equal (recycling works fine
for simple cases but always seems to trip me up in more
complicated cases).

Peter Ehlers


On 2012-07-26 07:02, Martin Ivanov wrote:
>
> Dear Peter,
>
> Thank You very much for your suggestion. However, it seems to me to make a
completely new notation to the x axis. While I just need to add minor ticks to
the axis, that is smaller ticks inbetween the basic ticks.
> The other option would be to say which ticks to be small and which big, but
I have no idea how.
>
> Any suggestions will be appreciated.
>
> Best regards,
>
> Martin
>
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