r - 在 rpart.plot 中格式化拆分标签

Question

我正在用 rpart.plot::prp() 绘制一棵树，很像:

library("rpart.plot")
data("ptitanic")
data <- ptitanic
data$sibsp <- as.integer(data$sibsp) # just to show that these are integers
data$age <- as.integer(data$age) # just to show that these are integers
tree <- rpart(survived~., data=data, cp=.02)
prp(tree, , fallen.leaves = FALSE, type=4, extra=1, varlen=0, faclen=0, yesno.yshift=-1)

即使某些变量是整数(age 和 sibsp)，rpart 也会创建一个看似任意的分割点，这会让观看者感到困惑。船上没有人有 2.5 个 sibling /配偶——逻辑分割是 sibsp >= 3

我在这个优秀的 tutorial 中查看了 split.fun和 ?prp。除了使用正则表达式来捕获数字、正确格式化并在标签字符串中替换它之外，我想不出 prp 中的任何解决方案。

我正在考虑的一个变通方法是传递修改后的树(类rpart 的对象)，其中的内容已四舍五入。是否可以通过修改 tree$splits 来做到这一点？

还有其他想法吗？

Answer 1

1) 有序因子 我认为 age 作为连续变量是可以的，但要处理 sibsp 和 parch将它们变成有序因子:

data <- transform(data, sibsp = ordered(sibsp), parch = ordered(parch))
tree <- rpart(survived~., data=data, cp=.02)
prp(tree, , fallen.leaves = FALSE, type=4, extra=1, varlen=0, faclen=0, yesno.yshift=-1)

2) split.fun 另一种方法是像这样指定我们自己的 split.fun:

# next 4 lines are same as in question
data <- ptitanic
data$sibsp <- as.integer(data$sibsp) # just to show that these are integers
data$age <- as.integer(data$age) # just to show that these are integers
tree <- rpart(survived~., data=data, cp=.02)

split.labs <- function(x, labs, digits, varlen, faclen) {
   sapply(labs, function(lab) 
      if (grepl(">=|<", lab)) {
         rhs <- sub(".* ", "", lab)
         lab <- sub(rhs, ceiling(as.numeric(rhs)), lab)
      } else lab)
} 
prp(tree, , fallen.leaves = FALSE, type=4, extra=1, varlen=0, faclen=0, yesno.yshift=-1, 
   split.fun = split.labs) # same as in question except for split.fun= arg

这给出:

(2a) (2) 的变体提供了更多的控制，即可以精确指定要修改的变量，如下所示:

# next 4 lines are same as in question
data <- ptitanic
data$sibsp <- as.integer(data$sibsp) # just to show that these are integers
data$age <- as.integer(data$age) # just to show that these are integers
tree <- rpart(survived~., data=data, cp=.02)

split.labs2 <- function(x, labs, digits, varlen, faclen) {
    sapply(labs, function(lab) 
        if (grepl("age|sibsp|parch", lab)) {
            rhs <- sub(".* ", "", lab);
            lab <- sub(rhs, ceiling(as.numeric(rhs)), lab)
        } else lab)
} 

# similar to (2) except we use clip.right.labs = FALSE and split.labs2

prp(tree, type = 4, fallen.leaves = FALSE, extra=1, varlen=0, faclen=0, 
   yesno.yshift=-1, clip.right.labs = FALSE, split.fun = split.labs2)