CHAID 包用途partykit http://cran.r-project.org/web/packages/partykit/(递归分区)树结构。您可以使用参与方节点遍历树 - 节点可以是终端节点,也可以具有包含有关决策规则(拆分)和拟合数据信息的节点列表。
下面的代码遍历树并创建决策表。它是为了演示目的而编写的,并且仅在一个示例树上进行了测试。
tree2table <- function(party_tree) {
df_list <- list()
var_names <- attr( party_tree$terms, "term.labels")
var_levels <- lapply( party_tree$data, levels)
walk_the_tree <- function(node, rule_branch = NULL) {
# depth-first walk on partynode structure (recursive function)
# decision rules are extracted for every branch
if(missing(rule_branch)) {
rule_branch <- setNames(data.frame(t(replicate(length(var_names), NA))), var_names)
rule_branch <- cbind(rule_branch, nodeId = NA)
rule_branch <- cbind(rule_branch, predict = NA)
}
if(is.terminal(node)) {
rule_branch[["nodeId"]] <- node$id
rule_branch[["predict"]] <- predict_party(party_tree, node$id)
df_list[[as.character(node$id)]] <<- rule_branch
} else {
for(i in 1:length(node)) {
rule_branch1 <- rule_branch
val1 <- decision_rule(node,i)
rule_branch1[[names(val1)[1]]] <- val1
walk_the_tree(node[i], rule_branch1)
}
}
}
decision_rule <- function(node, i) {
# returns split decision rule in data.frame with variable name an values
var_name <- var_names[node$split$varid[[1]]]
values_vec <- var_levels[[var_name]][ node$split$index == i]
values_txt <- paste(values_vec, collapse = ", ")
return( setNames(values_txt, var_name))
}
# compile data frame list
walk_the_tree(party_tree$node)
# merge all dataframes
res_table <- Reduce(rbind, df_list)
return(res_table)
}
使用 CHAID 树对象调用函数:
table1 <- tree2table(chaidUS)
结果应该是这样的:
gender ager empstat educr marstat nodeId predict
-------- -------------------------- --------- ------------------ -------------------------------- -------- ---------
NA NA NA <HS, HS, >HS married 3 Gore
NA NA NA College, Post Coll married 4 Bush
male NA NA NA widowed, divorced, never married 6 Gore
female 18-24, 25-34, 35-44, 45-54 NA NA widowed, divorced, never married 8 Gore
female 55-64, 65+ NA NA widowed, divorced, never married 9 Gore