Use (partykit- Nodeapply- Info_node) to extrac information within the function - function

Question

I am trying to extract information coming from nodeapply( info_node) function.
I want to automate the process so that I can extract the information of a list a node ids and operate on them later.
The example as follow:
data("cars", package = "datasets")
ct <- ctree(dist ~ speed, data = cars)
node5 <-nodeapply(as.simpleparty(ct), ids = 5, info_node)
node5$`5`$n
I use the code above to extract the number of records on node 5.
I want to create a function to extract the info from a series of node:
infonode <- function(x,y){
for (j in x){
info = nodeapply(y, j, info_node)
print(info$`j`$n)
}
}
But the result always comes back as null.
I wonder if the type of "J" is wrong within the function that leads to a null read in the print.
If someone could help me it would be greatly appreciated!
Thanks

Answer 1

You can give nodeapply() a list of ids and then not only list with a single element will be extracted but a list of all selected nodes. This is the only partykit-specific part of your question.
From that point forward it is simply operating on standard named lists in R, without anything partykit specific about that. To address your problem you can easily use [[ indexing rather than $ indexing, either with an integer or a character index:
node5[[1]]$n
## n
## 19
node5[["5"]]$n
## n
## 19
Thus, in your infonode() function you could replace info$j$n by either info[[1]]$n or info[[as.character(j)]]$n.
However, I would simply do this with an sapply():
ni <- nodeapply(as.simpleparty(ct), ids = 3:5, info_node)
sapply(ni, "[[", "n")
## 3.n 4.n 5.n
## 15 16 19
Or some variation of this...