Add two regression lines to plots in ggpairs

multi_smooth_ggpairs.R

require(datasets)
data("swiss")
require(GGally)
require(ggplot2)

my_fn <- function(data, mapping, ...){
  p <- ggplot(data = data, mapping = mapping) + 
    geom_point() + 
    geom_smooth(method=loess, fill="red", color="red", ...) +
    geom_smooth(method=lm, fill="blue", color="blue", ...)
  p
}

g = ggpairs(swiss,columns = 1:4, lower = list(continuous = my_fn))
g