Prp 图 - 以不同方式为正值和负值着色

Question

我正在通过函数 rpart() 拟合回归树。根据我的数据，我将对节点进行正负估计。有没有办法给它们涂上不同的颜色？

特别是，我想要的是一棵树，其节点以蓝色阴影表示负值，以红色阴影表示正值，其中颜色越深表示绝对值越强。

我附上一个最小的可重现示例。

library(rpart)
library(rpart.plot)

# Simulating data.
set.seed(1986)

X = matrix(rnorm(2000, 0, 1), nrow = 1000, ncol = 2) 
epsilon = matrix(rnorm(1000, 0, 0.01), nrow = 1000)

y = X[, 1] + X[, 2] + epsilon

dta = data.frame(X, y)

# Fitting regression tree.
my.tree = rpart(y ~ X1 + X2, data = dta, method = "anova", maxdepth = 3) 

# Plotting.
prp(my.tree,
    type = 2,
    clip.right.labs = FALSE,
    extra = 101,
    under = FALSE,
    under.cex = 1,
    fallen.leaves = TRUE,
    box.palette = "BuRd",
    branch = 1,
    round = 0,
    leaf.round = 0,
    prefix = "" ,
    main = "",
    cex.main = 1.5,
    branch.col = "gray",
    branch.lwd = 3)

# Repeating, with median(y) != 0.
X = matrix(rnorm(2000, 5, 1), nrow = 1000, ncol = 2) 
epsilon = matrix(rnorm(1000, 0, 0.01), nrow = 1000)
y = X[, 1] + X[, 2] + epsilon
dta = data.frame(X, y)

my.tree = rpart(y ~ X1 + X2, data = dta, method = "anova", maxdepth = 3) 

# HERE I NEED HELP!
prp(my.tree,
    type = 2,
    clip.right.labs = FALSE,
    extra = 101,
    under = FALSE,
    under.cex = 1,
    fallen.leaves = TRUE,
    box.palette = "BuRd",
    branch = 1,
    round = 0,
    leaf.round = 0,
    prefix = "" ,
    main = "",
    cex.main = 1.5,
    branch.col = "gray",
    branch.lwd = 3)

据我了解，由于box.palette选项，我在第一个设置中获得了我需要的结果，因为median(y)接近于零。

的确，在第二个设置中我很不高兴：对于小于 median(y) 的值，我得到蓝色阴影，对于高于该值的值，我得到红色阴影。如何将零作为两种颜色的阈值？

更具体地说，我想要一个自动确保任何树中双色系统的命令。

Answer 1

好的，我回答了我自己的问题。解决方案实际上很简单：如果 box.palette 选项是双色发散调色板（如我的示例），我们可以使用 pal.thresh 来设置我们想要的阈值。就我而言：

prp(my.tree,
    type = 2,
    clip.right.labs = FALSE,
    extra = 101,
    under = FALSE,
    under.cex = 1,
    fallen.leaves = TRUE,
    box.palette = "BuRd",
    branch = 1,
    round = 0,
    leaf.round = 0,
    prefix = "" ,
    main = "",
    cex.main = 1.5,
    branch.col = "gray",
    branch.lwd = 3,
    pal.thresh = 0) # HERE THE SOLUTION!

即使这可能对我不利，我也会在这里为未来的用户留下答案并关闭问题，而不是删除它。

Prp 图 - 以不同方式为正值和负值着色

Prp plot - Coloring positive and negative values differently

r

plot

tree

rpart