R help - Apr 2006 - Problem calling xyplot() within a function

Hi All
 
I'm fairly new at R so there might be on obvious solution to my problem
with calling the lattice function xyplot( ) from my own function.
 
The function script is given below.
 
The problem is that the xyplot() call does not do anything! I just get a
blank graphics window and no error messages.
 
The simple plot() function call works fine when not commented out so I
know the data is getting in OK and when I run the the same xyplot()
function call outside this function substituting the actual data frame
then xyplot( ) works fine. Comparing the data summary both inside and
outside the function showed that the data is identical. I put the
"require('lattice')" statement in because I thought it might
help but it
did'nt. 
 
Any help as to why xyplot() is behaving differently to plot() and what I
need to do to get the function working would be much appreciated.
 
thanks
 
Steve
 
------------------------------------------------------------------------
-----------
Steven G Candy
Applied Statistician
Australian Antarctic Division
203 Channel Highway, KINGSTON
Tasmania 7050
 
ph +61 3 6232 3135
 
"plot.fits.casal.trellis"<- function(data.df,xlim,ylim,XLAB,ylab) {

require('lattice')

frame( )

print(summary(data.df))

#plot(y=data.df$Mobs[data.df$year.f=="2004"],
x=data.df$Mage.r[data.df$year.f=="2004"],

# xlab = XLAB, ylab = ylab, ylim=ylim, xlim=xlim, type='p')

xyplot(data.df$Mobs+data.df$Mfit ~ data.df$Mage.r | data.df$year.f,
type=c("p","l"),pch=c("o","e"),cex=1.3,

xlab = XLAB, ylab = ylab, ylim=ylim, xlim=xlim) 

}


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Steve Candy wrote:
> Hi All
>  
> I'm fairly new at R so there might be on obvious solution to my problem
> with calling the lattice function xyplot( ) from my own function.
>  
> The function script is given below.
>  
> The problem is that the xyplot() call does not do anything! I just get a
> blank graphics window and no error messages.
>  
> The simple plot() function call works fine when not commented out so I
> know the data is getting in OK and when I run the the same xyplot()
> function call outside this function substituting the actual data frame
> then xyplot( ) works fine. Comparing the data summary both inside and
> outside the function showed that the data is identical. I put the
> "require('lattice')" statement in because I thought it
might help but it
> did'nt. 
>  
> Any help as to why xyplot() is behaving differently to plot() and what I
> need to do to get the function working would be much appreciated.
>  
<example snipped>

This is FAQ 7.22.

http://cran.r-project.org/doc/FAQ/R-FAQ.html

7.22 Why do lattice/trellis graphics not work?

The most likely reason is that you forgot to tell R to display the 
graph. Lattice functions such as xyplot() create a graph object, but do 
not display it (the same is true of Trellis graphics in S-Plus). The 
print() method for the graph object produces the actual display. When 
you use these functions interactively at the command line, the result is 
automatically printed, but in source() or inside your own functions you 
will need an explicit print() statement.

--sundar