[R] jpeg() creating empty files with qplot() in a loop

From: B. Bogart <bbogart_at_sfu.ca>
Date: Thu, 21 Feb 2008 10:51:33 -0800


Hello all,

I'm stuck with a strange issue with writing jpegs of plots to a folder in a loop.

This works:

for (step in 1:length(steps)) {
  jpeg(filename=paste("frame_",sprintf("%05d",step),".jpg",sep=""))   plot(steps[[step]])
  dev.off()
}

But if I use qplot to generate the plot (which is my aim):

for (step in 1:length(steps)) {
 jpeg(filename=paste("frame_",sprintf("%05d",step),".jpg",sep=""))  qplot(x, y, data=steps[[step]], geom="tile", fill=rgb(V1,V2,V3)) + scale_fill_identity() + opts(aspect.ratio = .75)  dev.off()
}

I end up with a directory of empty files named correctly.

The following does work:

step <- 10
jpeg(filename=paste("frame_",sprintf("%05d",step),".jpg",sep="")) qplot(x, y, data=steps[[step]], geom="tile", fill=rgb(V1,V2,V3)) + scale_fill_identity() + opts(aspect.ratio = .75) dev.off()

So what could be the difference between the last example and it running in a loop, that the former generates a proper jpeg file and the lattter does not?

Does something more special than dev.off() need to be done with qplot output when in a loop?

Thanks,
B. Bogart



R-help_at_r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Thu 21 Feb 2008 - 18:54:31 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Fri 22 Feb 2008 - 00:30:16 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.

list of date sections of archive