directlabels - utility.function - Positioning Method - extreme.points

Label the points furthest from the middle for each group.

extreme.points <- function(d,...){
  d$dist.from.center <- sqrt((d$x-midrange(d$x))^2+(d$y-midrange(d$y))^2)
  gapply(d,function(d,...)d[which.max(d$dist.from.center),])
}