How to position annotate text in the blank area of facet ggplot

问题

How to annotate some text in the blank space within a odd numbered faceted ggplot. Lets have a faceted ggplot with data as below with with 2 rows and 2 columns. So there is blank space in place of 2 row, 2nd column.

  df<- data.frame(Ara = rep("XTX", each = 3),
              Len = c(744, 750, 755),
              Mon = c("Sep", "Oct","Nov"),
              Value=c(11.224,10.15,4.23))
  df
  facetplot<-ggplot(df, aes(x=Value, y=Len, shape=Ara))+
      geom_point(size=5.0)+
      theme(legend.position = c(.7, .4), legend.direction="vertical")+
      facet_wrap(~Mon,scales="free_x", nrow=2)
  facetplot

Now i am trying to annotate some text in the space but could not ( as written in red in the image). I am looking for something similar to legend.position for annotated text. Do anyone has any idea on this.Or what would be the possible work around. Thank you.

回答1:

After you create your plot, simply use

print(facetplot)
grid.text("your text", x = 0.75, y = 0.25)

See ?grid.text for details on positioning. The default coordinate system is the entire screen device with (0,0) as the lower left and (1,1) as the upper right.

回答2:

To modify the graphical parameter setting for grid.text such as font color, family, fontface and size ...

grid.text("your text", x = 0.6, y = 0.15, gp = gpar(col="red", fontsize = 20, family = "Times", fontface = "italic"))

来源：https://stackoverflow.com/questions/29594348/how-to-position-annotate-text-in-the-blank-area-of-facet-ggplot