在使用caret包训练随机森林模型时,我注意到执行时间异常地长。
> set.seed = 1;
> n = 500;
> m = 30;
> x = matrix(rnorm(n * m), nrow = n);
> y = factor(sample.int(2, n, replace = T), labels = c("yes", "no"))
> require(caret);
> require(randomForest);
> print(system.time({rf <- randomForest(x, y);}));
user system elapsed
0.99 0.00 0.98
> print(system.time({rfmod <- train(x = x, y = y,
+ method = "rf",
+ metric = "Accuracy",
+ trControl = trainControl(classProbs = T)
+ );}));
user system elapsed
95.83 0.71 97.26
在我看来,执行时间应该只会增加10倍,因为默认情况下会进行10倍交叉验证而不是单次运行。虽然我没有调整任何参数,但似乎train会自动完成:
> rfmod$results
mtry Accuracy Kappa AccuracySD KappaSD
1 2 0.4736669 -0.04437013 0.03323485 0.06493845
2 16 0.4818095 -0.03241901 0.03279341 0.06426745
3 30 0.4878361 -0.02149108 0.02956972 0.05936881
这最多只能解释30倍的差别,但运行时间却长达100倍。可能的解释是什么呢?
提前感谢!
number = ifelse(grepl("cv", method), 10, 25), repeats = ifelse(grepl("cv", method), 1, number),`
- maksay