geom_function with facet_wrap

statfuns.R

library(dplyr)
library(ggplot2)

set.seed(123)
fdf <- expand_grid(year=1:4, generation=1:4) %>% 
  mutate(mu=rnorm(16),sigma=abs(rnorm(16)))


layerfun <- split(fdf, interaction(fdf$year, fdf$generation)) %>% 
  lapply(function(x){
    geom_function(data = x,
                  fun = dnorm,
                  args = list(mean=x$mu, sd=x$sigma),
                  aes(colour = factor(generation)))  
  })

ggplot(fdf) +
  layerfun +
  facet_wrap(~year, nrow = 5) +
  xlim(-4, 4)
ggsave("statfuns.png")