Generating random points per polygon feature proportional to each polygon feature area

Question

I am wondering what is the easiest way to generate random points per polygon feature using sp::spsample so that number of points in each feature is proportional to the corresponding polygon area. I know how to do it one a polygon but I am not sure how I should do it per feature.

Sample data

p <- shapefile(system.file("external/lux.shp", package="raster"))

Answer 1

One way to do this is as below:

library(raster)
library(sf)

set.seed(123)

# shape file from raster package
p <- shapefile(system.file("external/lux.shp", package="raster"))
plot(p)

# Using an old fashion for-loop
rpnt <- list()
for(i in 1:length(p)){
  pp <- p[p$ID_2==i,]
  rpnt[[i]] <- sp::spsample(pp, n=pp$AREA/20, "random") #modify it to what you want
  plot(rpnt[[i]], pch=i, col=(i), add=T)
}

out <- do.call(bind, rpnt)