directlabels - utility.function - Positioning Method - label.endpoints

Make a Positioning Method that labels a certain x value.

label.endpoints <- function
### Make a Positioning Method that labels a certain x value.
(FUN,
### FUN(d$x) should return an index of which point to label. for
### example you can use which.min or which.max.
 HJUST
### hjust of the labels.
 ){
  stopifnot(is.function(FUN))
  stopifnot(length(HJUST)==1)
  stopifnot(is.numeric(HJUST))
  stopifnot(is.finite(HJUST))
  function(d,...)gapply(d,function(d,...){
    i <- FUN(d$x)==d$x
    if(length(i)==0){
      data.frame()
    }else{
      sub.df <- d[i,]
      if(nrow(sub.df) > 1){
        y.target <- mean(range(sub.df$y))
        sub.df <- sub.df[1,]
        sub.df$y <- y.target
      }
      sub.df$hjust <- HJUST
      sub.df$vjust <- 0.5
      sub.df
    }
  })
### A Positioning Method like first.points or last.points.
}