[R] user coordinates and rug plots in lattice graphics

[John Fox]

Dear Deepayan,

Using current.viewport()$yscale does the trick -- for example:

     x <- rnorm(50)
     y <- rnorm(50)
     f <- factor(sample(c('a','b','c'),size=50, replace=T))
     par(tck = 0.03)
     z <- xyplot(y~x|f,
         panel = function(x,y,...) {
                 panel.xyplot(x,y,...)
                 ymin <- current.viewport()$yscale[1]
                 lpoints(x, rep(ymin, length(x)), pch="|", col='black')
         })
     z

Thank you very much,
  John

At 09:09 AM 4/8/2002 -0700, Deepayan Sarkar wrote:

>--- John Fox <jfox at mcmaster.ca> wrote:
> > Dear R list members,
> >
> > I'd like to produce rug plots at the bottom of panels in a trellis display
> > (using the lattice package), but par("usr") doesn't return user 
> coordinates
> > for panels, and consequently rug fails, as the following example 
> (suggested
> > to me by Georges Monette) illustrates:
> >
> >      > x <- rnorm(50)
> >      > y <- rnorm(50)
> >      > f <- factor(sample(c('a','b','c'),size=50, replace=T))
> >      > z <- xyplot(y~x|f,
> >      +        panel = function(x,y,...) {
> >      +                panel.xyplot(x,y,...)
> >      +                rug(x)
> >      +                print(par('usr'))
> >      +        })
> >      > z
> >      [1] 0 1 0 1
> >      [1] 0 1 0 1
> >      [1] 0 1 0 1
> >      Warning messages:
> >      1: some values will be clipped in: rug(x)
> >      2: some values will be clipped in: rug(x)
> >      3: some values will be clipped in: rug(x)
> >
> > (R Version 1.4.1 on a Windows 2000 PC.)
> >
> > This code runs properly in S-PLUS, by the way, where par("usr") returns
> > user coordinates when invoked within a panel function.
>
>The problem arises because lattice is based on grid graphics, and conventional
>R graphics do not work under grid. The way around (to get the user
>coordinates) here would be to use current.viewport()$xscale and
>current.viewport()$yscale (both should be vectors of length 2).
>
> > I don't see a way around the problem. If I could determine the minimum
> > value of y in a panel, I could make my own rug plot. Any help would be
> > greatly appreciated.
>
>For this, you might want to use lsegments. (This may be slow now, but should
>be faster in the next release.)

-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
-----------------------------------------------------

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