[R] pairs, panel.functions, xlim and ylim

[Valeria Edefonti]

Hi,

I have the following problem.
I wanted to get a matrix of scatterplots and I used pairs.
I wanted to add the line y=x in each plot and I created a panel 
function for this scope.
I used points and abline in the following way:

## put y=x in each plot
     panel.lin<- function(x, y)
     {
         points(x,y, pch=21, bg=par("bg"), col = "black",cex=2)
         abline(0,1,lwd=2, col="red")
     }

and it works.
Now, I want that each plot has the same scale on the axis and I try 
with this modification:

## put y=x in each plot - same scale for all the plots
     panel.lincor<- function(x, y)
     {
         points(x,y, pch=21, bg=par("bg"), col = 
"black",cex=2,xlim=c(-1,1),ylim=c(-1,1))
         abline(0,1,lwd=2, col="red")
     }

but R tells me that xlim and ylim couldn't be set in high level plot 
functions.
I try to use plot() instead of points, but I realized immediately that 
I can't use plot as a panel function.
I know I could have added xlim and ylim directly in pairs() function, 
if I hadn't had a panel function, but I need the line y=x in every plot 
and I don't know other ways to get it.
Any idea?
Thank you very much
Valeria Edefonti