Warning "Unknown or uninitialised column: `ntree`." when trying to pass hyperparameters to a learner with package mlr

Question

problem

I want to do a grid search with different hyperparameters that are provided by a self-made grid. But when I am running the code I get a warning: "Unknown or uninitialised column: ntree."

example data

age <- c(round(rnorm(120,mean = 50,sd = 10)))
sex <- c(round(rnorm(120,mean = 0.5,sd = 0.2)))
l1 <- as.logical(c(round(rnorm(120,mean = 0.5,sd = 0.2))))
l2 <- as.logical(c(round(rnorm(120,mean = 0.5,sd = 0.2))))
l3 <- as.logical(c(round(rnorm(120,mean = 0.5,sd = 0.2))))
l4 <- as.logical(c(round(rnorm(120,mean = 0.5,sd = 0.2))))
data <- as.data.frame(cbind(age,sex,l1,l2,l3,l4))

In reality I have 12 labels, but I left the others out to make it easier to look at. The idea is that l1 untill l4 are logical vectors. Somehow that doesn't work, so I hope you can fix that. But be aware that that is not my main question.

create grid

gs <- list(ntree = c(50,100,150,200,300,500,550),mtry = c(1,2,3,4,5)) %>% cross_df()

select hyperparameters

  for (h in 1:nrow(gs)) {
    ntree_entry <- gs$ntree[h]
    mtry_entry <- gs$mtry[h]
    (...)
    lrn <- makeMultilabelClassifierChainsWrapper(lrn, order = NULL) 
    lrn <- setPredictType(lrn,"prob")
    task <- makeMultilabelTask(data = data[train_lines,], target = label_bact) 
    mod <- mlr::train(lrn,task)
    }

On the place of (...) I have tried two different ways to get the hyperparameters into the learner:

option 1: pass hyperparameters to the learner

lrn <- makeLearner("classif.randomForest",ntree = ntree_entry,mtry = mtry_entry)

option 2: pass hyperparameters to the learner

lrn <- makeLearner("classif.randomForest")
lrn <- setHyperPars(lrn,par.vals = list(ntree = ntree_entry,mtry = mtry_entry))

check

The console tells me that the hyperparameters are in the learner:

>lrn
Learner classif.randomForest from package randomForest
Type: classif
Name: Random Forest; Short name: rf
Class: classif.randomForest
Properties: twoclass,multiclass,numerics,factors,ordered,prob,class.weights,oobpreds,featimp
Predict-Type: response
Hyperparameters: ntree=50,mtry=1

ntree and mtry are hyperparameters that are known to the makeLearner, because they are both in getParamSet:

> getParamSet("classif.randomForest")

                     Type  len   Def   Constr Req Tunable Trafo
ntree             integer    -   500 1 to Inf   -    TRUE     -
mtry              integer    -     - 1 to Inf   -    TRUE     -
replace           logical    -  TRUE        -   -    TRUE     -
classwt     numericvector <NA>     - 0 to Inf   -    TRUE     -
cutoff      numericvector <NA>     -   0 to 1   -    TRUE     -
strata            untyped    -     -        -   -   FALSE     -
sampsize    integervector <NA>     - 1 to Inf   -    TRUE     -
nodesize          integer    -     1 1 to Inf   -    TRUE     -
maxnodes          integer    -     - 1 to Inf   -    TRUE     -
importance        logical    - FALSE        -   -    TRUE     -
localImp          logical    - FALSE        -   -    TRUE     -
proximity         logical    - FALSE        -   -   FALSE     -
oob.prox          logical    -     -        -   Y   FALSE     -
norm.votes        logical    -  TRUE        -   -   FALSE     -
do.trace          logical    - FALSE        -   -   FALSE     -
keep.forest       logical    -  TRUE        -   -   FALSE     -
keep.inbag        logical    - FALSE        -   -   FALSE     -

Question

Why do I get the message "Unknown or uninitialised column: ntree"? Although it is only a warning, not an error, I am afraid that it will only use the first line of the grid that I created. The size of the models seem to confirm that. They all have the same size. I hope that someone can help me with this problem. Thanks in advance!