Using geom_rect for time series shading in R

Question

I am trying to shade a certain section of a time series plot (a bit like recession shading - similarly to the graph at the bottom of this article on recession shading in exc

Answer 1

To use geom_rect you need to define your rectangle coordinate through a data.frame:

shade = data.frame(x1=c(1918,1930), x2=c(1921,1932), y1=c(-3,-3), y2=c(4,4))

#    x1   x2 y1 y2
#1 1918 1921 -3  4
#2 1930 1932 -3  4

Then you give ggplot your data and the shade data.frame:

ggplot() + 
  geom_line(aes(x=month, y=big), color='red',data=a_series_df)+
  geom_rect(data=shade, 
            mapping=aes(xmin=x1, xmax=x2, ymin=y1, ymax=y2), color='grey', alpha=0.2)