R:使用带有插入符号的ranger,tuneGrid参数

Question

我正在使用插入包来分析使用游侠构建的随机森林模型.我无法弄清楚如何使用tuneGrid参数调用train函数来调整模型参数.

我想我调用了tuneGrid参数是错误的,但是无法弄清楚为什么它是错误的.任何帮助,将不胜感激.

data(iris)

library(ranger)
model_ranger <- ranger(Species ~ ., data = iris, num.trees = 500, mtry = 4,
                       importance = 'impurity')


library(caret)

# my tuneGrid object:
tgrid <- expand.grid(
  num.trees = c(200, 500, 1000),
  mtry = 2:4
)

model_caret <- train(Species  ~ ., data = iris,
                     method = "ranger",
                     trControl = trainControl(method="cv", number = 5, verboseIter = T, classProbs = T),
                     tuneGrid = tgrid,
                     importance = 'impurity'
)

Answer 1

以下是插入符号中的游侠语法:

library(caret)

.在调整参数之前添加:

tgrid <- expand.grid(
  .mtry = 2:4,
  .splitrule = "gini",
  .min.node.size = c(10, 20)
)

插入符号只支持这三种,而不是树木的数量.在火车上你可以指定num.trees和important:

model_caret <- train(Species  ~ ., data = iris,
                     method = "ranger",
                     trControl = trainControl(method="cv", number = 5, verboseIter = T, classProbs = T),
                     tuneGrid = tgrid,
                     num.trees = 100,
                     importance = "permutation")

获得变量重要性:

varImp(model_caret)

#output
             Overall
Petal.Length 100.0000
Petal.Width   84.4298
Sepal.Length   0.9855
Sepal.Width    0.0000

要检查这是否有效,将树的数量设置为1000+ - 拟合将慢得多.更改后importance = "impurity":

#output:

             Overall
Petal.Length  100.00
Petal.Width    81.67
Sepal.Length   16.19
Sepal.Width     0.00

如果它不起作用,我建议从CRAN安装最新的游侠,从git hub安装插入符号:

devtools::install_github('topepo/caret/pkg/caret')

训练树木的数量,您可以使用lapply由createMultiFolds或创建的固定折叠createFolds.