~ 的功能/意义。 用于插入符号 R 包中的训练功能

Question

train(Class ~ ., data = training, 
                 method = "gbm", 
                 trControl = fitControl,
                 ## This last option is actually one
                 ## for gbm() that passes through
                 verbose = FALSE)

I know that Class is predictor but what i do not understand is meaning/need of ~ .

Any help or pointers towards help will be highly appreciated.

PS. I am new to R

Answer 1

This means anything else except medv (in this example) like the normal usage in a formula. Basically you're predicting against all predictors in the dataset. Take for instance this:

library(caret)
library(mlbench)
data(BostonHousing)
lmFit <- train(medv ~ . + rm:lstat,
               data = BostonHousing,
               method = "lm")

To see the terms call lmFit$terms . Of significance is this:

medv ~ crim + zn + indus + chas + nox + rm + age + dis + rad + 
    tax + ptratio + b + lstat + rm:lstat

You can exclude like so:

lmFit <- train(medv ~.-zn -so on -so on  + rm:lstat,
               data = BostonHousing,
               method = "lm")