Add margins with grid R package

Question

I don't know how to specify margins for PDF printing with grid R package.

I create a grid.arrange() object and I put it in a PDF like this :

pdf('test.pdf',11.69,8.27)
grid.arrange(textGrob('text1', gp=gpar(cex=4)),
             ncol=1, main=textGrob('title', gp=gpar(cex=1.5)),
             widths = c(1), heights = c(1))
dev.off()

But the title is push at the top edge of the sheet. I would like to add margins. If I add a textGrob instead of the main= function for the title, I can keep it away from the top but it's not a solution for me because I have to put graphs and they are close to the edge too.

Answer 1

arrangeGrob has a viewport argument,

vp = viewport(height=unit(0.8, "npc"), 
                          width=unit(5, "cm"))

g = arrangeGrob(textGrob('text1', gp=gpar(cex=4)),
              top = textGrob('title', gp=gpar(cex=1.5)),  
              vp=vp)
grid.newpage()
grid.rect(vp=vp)
grid.draw(g)