R help - Dec 2007 - both lines and plot characters in a lattice plot key

Hello,

I have two short questions concerning a key (legend) in a lattice  
plot. I have points represented by two different plot characters  
(crosses and circles) and they are colored from light to dark gray. I  
would like to have 3 parts in my legend showing the two different  
plot characters in the first two lines and the last line should  
consist of a line segment for explaining the different shades of  
gray. Below you can see what I reached so far.
My first problem is, that I do not get the 2 plot characters and the  
line segment vertically aligned to each other (I chose the vector of  
plotting characters to contain "26" as last element, because this  
leaves out a plotting character for the last line, where the line  
segment should be placed). So how do I get these aligned?
My second question is, if it's possible to have a line segment shown  
in the key, which is colored from light to dark gray (instead of a  
single color), matching the colors in my specified variable "colors"  
if possible, i.e. a single line segment starting from light gray and  
ending with a dark gray.

Thanks very much in advance!

Jan

library(lattice)
x=c(1,2,3,4,5)
y=c(5,4,3,2,1)
symbolvec=c(3,3,3,1,3)
colorseq=seq(0.25,0.88,length=5)
colors=gray(colorseq)
colorvec=colors
xyplot(y~x,
	panel=function(...){
		panel.xyplot(...,type="n")
		lpoints(x,y,pch=symbolvec,col=colorvec)
	},
key=list(x=0.2,y=0.2,lines=list(lty=c(0,0,1)),points=list(pch=c 
(1,3,26)),text=list(c("key 1","key 2","key
3")),align=T,transparent=T))

On 12/25/07, Hofert Marius <m_hofert at web.de>
wrote:
> Hello,
>
> I have two short questions concerning a key (legend) in a lattice
> plot. I have points represented by two different plot characters
> (crosses and circles) and they are colored from light to dark gray. I
> would like to have 3 parts in my legend showing the two different
> plot characters in the first two lines and the last line should
> consist of a line segment for explaining the different shades of
> gray. Below you can see what I reached so far.
> My first problem is, that I do not get the 2 plot characters and the
> line segment vertically aligned to each other (I chose the vector of
> plotting characters to contain "26" as last element, because this
> leaves out a plotting character for the last line, where the line
> segment should be placed). So how do I get these aligned?
The 'lines' components allow a 'type' specification, so:

       key        list(x=0.2,y=0.2,
            lines=list(pch=c(1,3,1), type = c("p", "p",
"l")),
            text=list(c("key 1","key 2","key 3")),
            align=T,transparent=T)
> My second question is, if it's possible to have a line segment shown
> in the key, which is colored from light to dark gray (instead of a
> single color), matching the colors in my specified variable
"colors"
> if possible, i.e. a single line segment starting from light gray and
> ending with a dark gray.
Unfortunately, no, at least not using the 'key' argument.  However,
using the 'legend' argument gives you more flexibility, especially if
you are willing to write some grid code. Even without grid, you can
use draw.key() and draw.colorkey() together to produce one legend for
the plotting characters and a different one for the color gradient.

-Deepayan
>
> Thanks very much in advance!
>
> Jan
>
> library(lattice)
> x=c(1,2,3,4,5)
> y=c(5,4,3,2,1)
> symbolvec=c(3,3,3,1,3)
> colorseq=seq(0.25,0.88,length=5)
> colors=gray(colorseq)
> colorvec=colors
> xyplot(y~x,
>         panel=function(...){
>                 panel.xyplot(...,type="n")
>                 lpoints(x,y,pch=symbolvec,col=colorvec)
>         },
> key=list(x=0.2,y=0.2,lines=list(lty=c(0,0,1)),points=list(pch=c
> (1,3,26)),text=list(c("key 1","key 2","key
3")),align=T,transparent=T))
>
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