Extract Node List from Tree Model

Extracts node-level attributes from a tree model object. Node IDs are the binary heap indices from rownames(input_object$frame) and match the from/to values produced by edgelist.tree, so the two outputs can be passed directly to igraph::graph_from_data_frame().

Usage

# S3 method for class 'tree'
nodelist(input_object, ...)

Arguments

input_object

A tree model object from the tree package

...

Additional arguments (currently unused)

Value

A data.frame with one row per node and the following columns:

name

Integer node ID (binary heap index, matches edgelist from/to)

var

Split variable name, or "<leaf>" for terminal nodes

n

Number of observations routed to this node

dev

Deviance (impurity) at this node

yval

Predicted value (numeric for regression, character for classification)

is_leaf

Logical: TRUE for terminal nodes

depth

Integer tree depth (root = 0)

dev_improvement

Numeric deviance reduction from this node's split (NA for leaves)

prob_*

(Classification only) One column per class with the class probability at that node, named prob_<classname>. Class names are sanitized via make.names() and lowercased.

label

Display label: "<var>\nn=<n>" for internal nodes, "<yval>\nn=<n>" for leaves

Examples

if (requireNamespace("tree", quietly = TRUE)) {
  tr <- tree::tree(Species ~ Sepal.Length + Sepal.Width, data = iris)
  nodelist(tr)

  # Labels ready for plotting
  nodelist(tr)$label
}
#>  [1] "Sepal.Length\nn=150" "Sepal.Width\nn=59"   "Sepal.Length\nn=12" 
#>  [4] "versicolor\nn=5"     "versicolor\nn=7"     "Sepal.Length\nn=47" 
#>  [7] "setosa\nn=39"        "setosa\nn=8"         "Sepal.Width\nn=91"  
#> [10] "Sepal.Length\nn=86"  "versicolor\nn=37"    "Sepal.Length\nn=49" 
#> [13] "virginica\nn=39"     "virginica\nn=10"     "setosa\nn=5"