cforest prints empty tree

Question

I\'m trying to use cforest function(R, party package).

This\'s what I do to construct forest:

library(\"party\")
set.seed(42)
readingSkills.cf <-          


        

Answer 1

Short answer: the case weights weights in each node are NULL, i.e. not stored. The prettytree function outputs weights = 0, since sum(NULL) equals 0 in R.

---

Consider the following ctree example:

library("party")
x <- ctree(Species ~ ., data=iris)
plot(x, type="simple")

For the resulting object x (class BinaryTree) the case weights are stored in each node:

R> sum(x@tree$left$weights)
[1] 50
R> sum(x@tree$right$weights)
[1] 100
R> sum(x@tree$right$left$weights)
[1] 54
R> sum(x@tree$right$right$weights)
[1] 46

Now lets take a closer look at cforest:

y <- cforest(Species ~ ., data=iris, control=cforest_control(mtry=2))
tr <- party:::prettytree(y@ensemble[[1]], names(y@data@get("input")))
plot(new("BinaryTree", tree=tr, data=y@data, responses=y@responses))

The case weights are not stored in the tree ensemble, which can be seen by the following:

fixInNamespace("print.TerminalNode", "party")

change the print method to

function (x, n = 1, ...)·                                                     
{                                                                             
    print(names(x))                                                           
    print(x$weights)                                                          
    cat(paste(paste(rep(" ", n - 1), collapse = ""), x$nodeID,·               
        ")* ", sep = "", collapse = ""), "weights =", sum(x$weights),·        
        "\n")                                                                 
} 

Now we can observe that weights is NULL in every node:

R> tr
1) Petal.Width <= 0.4; criterion = 10.641, statistic = 10.641
 [1] "nodeID"     "weights"    "criterion"  "terminal"   "psplit"    
 [6] "ssplits"    "prediction" "left"       "right"      NA          
NULL
  2)*  weights = 0 
1) Petal.Width > 0.4
  3) Petal.Width <= 1.6; criterion = 8.629, statistic = 8.629
 [1] "nodeID"     "weights"    "criterion"  "terminal"   "psplit"    
 [6] "ssplits"    "prediction" "left"       "right"      NA          
NULL
    4)*  weights = 0 
  3) Petal.Width > 1.6
 [1] "nodeID"     "weights"    "criterion"  "terminal"   "psplit"    
 [6] "ssplits"    "prediction" "left"       "right"      NA          
NULL
    5)*  weights = 0 

Update this is a hack to display the sums of the case weights:

update_tree <- function(x) {
  if(!x$terminal) {
    x$left <- update_tree(x$left)
    x$right <- update_tree(x$right)
  } else {
    x$weights <- x[[9]]
    x$weights_ <- x[[9]]
  }
  x
}
tr_weights <- update_tree(tr)
plot(new("BinaryTree", tree=tr_weights, data=y@data, responses=y@responses))