How to label each node in a dendrogram based on label for the children using R

Question

I have a dendrogram in R where each leaf has a value. I like to define each node's value by summing the value of its children. I am familiar with dendrapply, however I don't know how to access a node's child in the function and how to write the function recursively.

here is the code to begin with:

library("stats")
library("fastcluster")
library("cluster")
D = rbind( + c(1,1,1,1,1), 
 + c(1,2,1,1,1),
 + c(2,2,2,2,2), 
 + c(3,4,5,6,9)

)
dnd = as.dendrogram(hclust.vector(D))

apply_text <<- function(n) {
   if (!is.leaf(n)) {

      attr(n, "edgetext") <- add the value of the branches
   }
   if (is.leaf(n)) {
      attr(n, "edgetext") <- 1
   }
   n
}

tmp <- dendrapply(dnd, apply_text)
plot(tmp)

Answer 1

This may be an answer, however, it is reimplementing the dendrapply.

apply_text <<- function(n){
  if (!is.leaf(n)) {
    cutversion = cut(n, h = attributes(n)$height)
    leftLabel = attr(apply_text(cutversion$lower[[1]]), "edgetext")  
    rightLabel= attr(apply_text(cutversion$lower[[2]]), "edgetext")
    attr(n, "edgetext") = as.numeric(as.character(leftLabel)) + as.numeric(as.character(rightLabel)) 
     }
  if(is.leaf(n)) {
    attr(n,"edgetext") <- 1
  }
    n
}

tmp <- dendrapply(dnd, apply_text)

Does anybody have a clue how to remove the polygon on the labels? Somebody else also seems to have asked for them to be removed. Any progress on that?