R help - Oct 2009 - Cairo package, png files within for loop are black?

Hello,

I am generating .png images using the Cairo package in a for loop 
(looping on the number of zones, number of zones equals the number of 
plots to create based on different zone data).   When  I run the R 
script the .png files are created but they are all black?  If I comment 
out the for loop and force my zones to equal one the png file is created 
correctly?  Is there an issue with generating .png files within a for loop?

Create .png commands within for loop:

CairoPNG(paste(t.g), width=800, height=600, pointsize=12, bg="white")
    xyplot(areasqmi ~ value, x.p, groups=dur,
    main=(t.n), ylab=expression("Area(mi" ^ 2 * ")"),
    xlab="Maximum Average Depth of Percipitation (inches)",
    scales=list(y=list(log=TRUE)), ylim=c(1,1000000), type='l',
    auto.key=list(space='right'))
dev.off()

-- 
---------------------------------
Douglas M. Hultstrand, MS
Senior Hydrometeorologist
Metstat, Inc. Windsor, Colorado
voice: 970.686.1253
email: dmhultst at metstat.com
web: http://www.metstat.com

On Thu, Oct 22, 2009 at 12:46 PM, Douglas M. Hultstrand
<dmhultst at metstat.com> wrote:
> Hello,
>
> I am generating .png images using the Cairo package in a for loop (looping
> on the number of zones, number of zones equals the number of plots to
create
> based on different zone data). ? When ?I run the R script the .png files
are
> created but they are all black? ?If I comment out the for loop and force my
> zones to equal one the png file is created correctly? ?Is there an issue
> with generating .png files within a for loop?
Probably not.  The behavior you observe is due to a lattice graphics
function being called in a loop.  When called within a loop you must
"print" or "show" the result of a lattice graphics function.
See FAQ
7.22
> Create .png commands within for loop:
>
> CairoPNG(paste(t.g), width=800, height=600, pointsize=12,
bg="white")
> ? xyplot(areasqmi ~ value, x.p, groups=dur,
> ? main=(t.n), ylab=expression("Area(mi" ^ 2 * ")"),
> ? xlab="Maximum Average Depth of Percipitation (inches)",
> ? scales=list(y=list(log=TRUE)), ylim=c(1,1000000), type='l',
> ? auto.key=list(space='right'))
> dev.off()
>
> --
> ---------------------------------
> Douglas M. Hultstrand, MS
> Senior Hydrometeorologist
> Metstat, Inc. Windsor, Colorado
> voice: 970.686.1253
> email: dmhultst at metstat.com
> web: http://www.metstat.com
>
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