[R] location of key in panels of trellis plot

[Paul Murrell]

Hi

Here's a modification of your panel function that I think does what you 
want (comments embedded):

tmp.xyplot <- function(x,y,subscripts=subscripts,cdata=cdata){
     # plot data points
     panel.xyplot(x,y)
     # extract parameter values
     right <- as.character(cdata[subscripts,][1,c(4,5,6)])
     #### Create the key for the panel
     key <- draw.key(list(text=list(expression(t[1],t[infinity],"p")),
                          text=list(c("=","=","=")),
                          text=list(right),
                          between=c(0.4),
                          rep=FALSE,
                          columns=1,
                          column.between=0),
                     draw=FALSE)
     #### Push a viewport in the top-right corner which is
     #### big enough to fit the key
     #### Uses grobWidth() and grobHeight() to get the size of the key
     #### (You'll need a library(grid) somewhere to direct access
     ####  to these grid functions)
     pushViewport(viewport(x=1, y=1,
                           width=grobWidth(key),
                           height=grobHeight(key),
                           just=c("right", "top")))
     #### Draw the key
     grid.draw(key)
     #### Pop the key viewport
     popViewport()
}

Hope that helps

Paul


Steven Lacey wrote:
> Hi,
> 
>  
> 
> I want to insert a key into each panel of a trellis plot, which I can do
> with a custom panel function that calles draw.key. The problem arises
> because I want the top right hand corner of the key to start in the top
> right hand corner of the panel. If you run my code below, you can see that
> the key appears in the center of each panel. This is because the default
> viewport in draw.key is the same size as the panel. I can readily change the
> height and width of the viewport such that only the key will fit (i.e.,
> viewport and key are the same size). While this works, it is not a robust
> solution. For example, if I change cex or resize, then I have to guess again
> what size viewport will be needed to fit only the key. How can I specify a
> viewport size that will always only fit the key itself? If I could do that,
> then I could have much more robust control over the key's position on the
> panel. That is, I could always specify the top right corner of the key to be
> at top right corner of the panel. 
> 
>  
> 
> In other words, if I had access to the width and height of the key in "npc"
> coordinates I could specify that in my viewport argument. But, I don't know
> how to access them without making a series of guesses.
> 
>  
> 
> Below is example code. 
> 
>  
> 
> Thanks, 
> Steve 
> 
>  
> 
> #### build a dataframe
> 
> dataframe<-data.frame(condition=factor(rep(c("A","B","C","D"),c(40,40,40,40)
> ),levels=c("A","B","C","D")),
> 
>                       var1=rnorm(160),
> 
>                       var2=rep(c(1:40),4),
> 
>                       parm1=rep(c(987.54,754,887.654,902),c(40,40,40,40)),
> 
>  
> parm2=rep(c(254.89,376.001,308,297.102),c(40,40,40,40)),
> 
>                       parm3=rep(c(0.2,38.5,1.5,0.654),c(40,40,40,40)))
> 
>  
> 
> ####Use xyplot to plot var1 against var2 for each condition. No problem. 
> 
> xyplot(var1~var2|condition,data=dataframe,ylim=c(4,-4))
> 
>  
> 
> ####Now I want to add a key to each panel indicating the values on the
> parameters 1-3.
> 
> ####To do so I write my own panel function that calls draw.key
> 
>  
> 
> tmp.xyplot <- function(x,y,subscripts=subscripts,cdata=cdata){
> 
>     # plot data points
> 
>     panel.xyplot(x,y)
> 
>     
> 
>     # extract parameter values
> 
>     right <- as.character(cdata[subscripts,][1,c(4,5,6)])
> 
>  
> 
>     #### draw the key on the panel
> 
>     draw.key(list(text=list(expression(t[1],t[infinity],"p")),
> 
>                   text=list(c("=","=","=")),
> 
>                   text=list(right),
> 
>                   between=c(0.4),
> 
>                   rep=FALSE,
> 
>                   columns=1,
> 
>                   column.between=0),
> 
>                   draw=TRUE)   
> 
>  
> 
> }
> 
>  
> 
> #### call xyplot with tmp.xyplot panel function
> 
> xyplot(var1~var2|condition,data=dataframe,ylim=c(4,-4),panel=tmp.xyplot,cdat
> a=dataframe)
> 
> 
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> 
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-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/