r - 使用partykit中的ctree为每个终端节点获取从叶子到根的完整路径

Question

我目前正在使用 R 包“partykit”中的 ctree，我想知道是否有办法获得从终端节点到根的完整路径。我希望每个叶子都有到根的完整路径，表示为包含节点 ID 的向量。

library(partykit)
ct <- ctree(Species ~ ., data = iris) 

Model formula:
Species ~ Sepal.Length + Sepal.Width + Petal.Length + Petal.Width

Fitted party:
[1] root
|   [2] Petal.Length <= 1.9: setosa (n = 50, err = 0.0%)
|   [3] Petal.Length > 1.9
|   |   [4] Petal.Width <= 1.7
|   |   |   [5] Petal.Length <= 4.8: versicolor (n = 46, err = 2.2%)
|   |   |   [6] Petal.Length > 4.8: versicolor (n = 8, err = 50.0%)
|   |   [7] Petal.Width > 1.7: virginica (n = 46, err = 2.2%)

Number of inner nodes:    3
Number of terminal nodes: 4

绘制树

这基本上是我需要的：

[[1]]
[1] 2 1

[[2]]
[1] 5 4 3 1

[[3]]
[1] 6 4 3 1

[[4]]
[1] 7 3 1

我将不胜感激任何帮助！谢谢！

Answer 1

The following function should do the trick. The first line extracts a list of kids per node and from this you can recursively go through all nodes.

get_path <- function(object) {
  ## list of kids per node (NULL if terminal)
  kids <- lapply(as.list(object$node), "[[", "kids")

  ## recursively add node IDs of children
  add_ids <- function(x) {
    ki <- kids[[x[1L]]]
    if(is.null(ki)) {
      return(list(x))
    } else {
      x <- lapply(ki, "c", x)
      return(do.call("c", lapply(x, add_ids)))
    }
  }
  add_ids(1L)
}

This can then be applied to any party object:

get_path(ct)
## [[1]]
## [1] 2 1
## 
## [[2]]
## [1] 5 4 3 1
## 
## [[3]]
## [1] 6 4 3 1
## 
## [[4]]
## [1] 7 3 1