从R中的多个JPEG生成PDF

Question

I have a folder with multiple JPEG files. How do I generate a PDF file from these JPEGs in R?

One JPEG = 1 PDF page. Images are of the same size.

Thanks a lot in advance.

Answer 1

You can do this easily using Latex. Which is nice, because then you can just use Sweave to do the whole thing.

You can do something along the lines of :

% This is some Sweave file
\documentclass{article}
\usepackage{graphicx}
\begin{document}

<<results=tex,echo=FALSE>>=
mypics <- dir('mypics')
for(i in mypics){
cat("\\includegraphics{", i, "}\n\n", sep = "")
}
@
\end{document}

OK, you'll have to set up your Sweave pipeline, but with a bit of tweaking you can automate the whole process easily.

Answer 2

If you insist on using R to do this then you can open a pdf plotting device, par to set the margins (default will probably be to big and not centering), then in a loop use plot.new to start a new page and plot.window to set up the coordinates, etc. without plotting axes etc., use the read.jpeg function from the ReadImages package (or other tool/package to read, EBImage is another possibility) then rasterImage to plot the jpeg to the pdf device (or replace some of those steps with other image plotting functions, such as the plot method in ReadImages).

But overall it is probably easier/quicker/better/... to use a tool better designed for this type of thing. The ImageMagick suite of programs comes to mind, LaTeX has also been mentioned, and there are probably other tools as well.

Answer 3

if you insist on using R (other tools are more suitable), try something like this (slow, untested):

   lf = list.files(pattern = "jpeg") # image filenames

   library(jpeg)
   jpegs = lapply(lf, readJPG)

   library(grid)
   pdf("output.pdf", width=8, height=4)
   grid.raster(jpegs[[1]])
   lapply(jpegs[-1], function(x) {grid.newpage() ; grid.raster(x)} ) -> bquiet
   dev.off()