All the trees from randomForest-model are use all the attributes of object, but not only mtry?

Question

I have trained model for classification task in R using randomForest - "RF_Model"

RF_Model <- randomForest(measure ~., data = dat), mtry=3, importance=TRUE,ntree=500)
print(RF_Model)

returns:

Call: randomForest(formula = measure ~ ., data = dat) Type of random forest: classification Number of trees: 500 No. of variables tried at each split: 3

Each object, which uses in that model, has 15 attributes. In my understanding (the basic knowledge I have got from here): mtry = number of random variables used in each tree. So, I thought, that for each sample decision tree (from those 500 trees in the forest) will be used only 3 different attributes from 15.

But when I tried to check that - I found that all the 15 attributes are used for each tree in the forest:

k <- 209 #tried here distinct values from 1 to 500
tree <- getTree(RF_Model, k, labelVar = TRUE)

and as the result, tree returns the tree with 19-27 levels of depth, and always all the 15 attributes are used for the tree.

What I am doing wrong or misunderstood? Why for the small trees in the forest (No. of variables tried at each split: 3) have been used not 3 distinct attributes, but always all 15?

Answer 1

Each object, which uses in that model, has 15 attributes. In my understanding (the basic knowledge I have got from https://www.listendata.com/2014/11/random-forest-with-r.html): mtry = number of random variables used in each tree. So, I thought, that for each sample decision tree (from those 500 trees in the forest) will be used only 3 different attributes from 15.

This is incorrect. mtry is the number of variables tried at each split. A nice introduction to random-forest can be found in Elements of Statistical Learning.