In R, how can I store an inset graph for later arranging it with grid.arrange?

问题

I have created a graph in which I inset another graph (both ggplot2 objects) via this command:

    vp=viewPort(...)
    print(ggplotobject1)
    print(ggplotobject2, vp=vp)

This works exactly how I'd like it to (one large graph with a custom small graph drawn in the area specified in viewPort).

The problem is that I need to use this combined graph later for arranging it with other plots again through:

grid.arrange(arrangeGrob(..))

Does anyone have an idea how I can store my combined graph as a grob?

Thank you very much indeed!

EDIT: Responding to baptiste here is a reproducible example:

library(ggplot2)
library(gtable)
library(grid)

data<-mtcars
main_plot<-ggplot(data,aes(hp,mpg,group=cyl))+
  geom_smooth(method="lm")+geom_point()+
  facet_grid(.~gear)
sub_plot<-ggplot(data,aes(disp,wt,color))+geom_point()

gtable_main<-ggplot_gtable(ggplot_build(main_plot))
gtable_sub<-ggplot_gtable(ggplot_build(sub_plot))
gtable_show_layout(gtable_main)
gtable_main2<-gtable_add_grob(gtable_main,gtable_sub,t=4,l=4,b=1,r=1) 
grid.draw(gtable_main2)

This produces the graph I want, but I fail to make the subplot the right size (it's supposed to be a small graph in the bottom left corner of the plot). This is probably really basic, but I haven't worked with gtable before and only a little bit with grid/gridExtra.

Thanks a lot!

回答1:

you could use annotation_custom or edit the gtable instead of printing to different viewports.

gm <- ggplotGrob(main_plot)
gs <- ggplotGrob(sub_plot)

library(gtable)
library(grid)
panel.id <- 1
panel <- gm$layout[gm$layout$name == "panel",][panel.id,]

inset <- grobTree(gs, vp=viewport(width=unit(1,"in"), x=0.8, y=0.8,
                                  height=unit(1,"in")))
gm <- gtable_add_grob(gm, inset, l=panel$l, t=panel$t)
grid.newpage()
grid.draw(gm)

来源：https://stackoverflow.com/questions/33305106/in-r-how-can-i-store-an-inset-graph-for-later-arranging-it-with-grid-arrange