[R] Common keys on separate lattice plots

[Deepayan Sarkar]

On Monday 02 December 2002 07:56 pm, Patrick Connolly wrote:
> In 'normal' plotting, by using text(.... outer = TRUE), I can set a
> title that can refer to multiple plots.
>
> I'm trying to achieve a similar effect with several trellis objects
> with which I wish to use a common key.  I can only think of
> complicated ways of achieving such an end by using a separate grid
> graphic which didn't have any plot, but text only.
>
> Is there something more elegant?

I'm guessing that you are positioning your plots by calling print.trellis 
explicitly with the position/split argument. Once these are complete, the 
whole plotting region should be the default viewport, so you could simply use 
grid.text to write your title. for example,

foo <- xyplot(...)

print(foo, position = c(0,0,.5,.8), more = TRUE)
print(foo, position = c(.5,0,1,.8), more = FALSE)
grid.text("Title", x = .5, y = .9) 

If by key you mean a legend (as produced by 'key' in a lattice call), you 
could use something like

draw.key(key = list(rect = list(col = 1:3)), 
         draw = TRUE, 
         vp = viewport(x=.5, y=.9))  

In either case, you would have to position the initial plots so that enough 
space is left.

Hope that helps.

-Deepayan