R graph quality

Question

Is there a way to optimize the graph quality from R?

I have 30 million data points, and I generated a Q–Q plot and saved it as a PDF file using:

pdf(myPlot.pdf)
qqnorm(X)
dev.off()

But the PDF file size is so big that I can not even open it to view!

Is there a way either saving this with a lower quality or as a different type (I don't necessarily need PDF) so I can view the graph?

Answer 1

You have a few options.

1. Don't plot all the points. Compare:

   X = rnorm(1e5)
   qqnorm(X, xlim=c(-4.5, 4.5), ylim=c(-4.5, 4.5))
   qqnorm(X[seq(1, length(X), 5)], xlim=c(-4.5, 4.5), ylim=c(-4.5, 4.5))
   qqnorm(X[seq(1, length(X), 10)], xlim=c(-4.5, 4.5), ylim=c(-4.5, 4.5))
   

   I would suggest it's almost impossible to visually notice a difference

2. Don't use the pdf plotting device. Instead try png or jpeg. These functions have a resolution argument, res, that controls the plotting resolution. So something like this should do the trick:

   ppi = 300
   png("mygraph.png", width=6*ppi, height=6*ppi, res=ppi)
   qqnorm(X)
   dev.off()