Adding stat_smooth in to only 1 facet in ggplot2

Question

I have some data for which, at one level of a factor, there is a significant correlation. At the other level, there is none. Plotting these side-by-side is simple. Adding a l

Answer 1

Don't think about picking a facet, think supplying a subset of your data to stat_smooth:

ggplot(df, aes(x, y)) +
  geom_point() + 
  geom_smooth(data = subset(df, z =="a")) + 
  facet_wrap(~ z)