Tuners

Popular black-box optimization techniques are implemented in the bbotk package. The corresponding connectors to for tuning hyperparameters of learners or pipelines reside as Tuner objects in package mlr3tuning. Additionally, packages mlr3hyperband and mlr3mbo provide some modern and sophisticated approaches.

All tuners operator on box-constrained tuning spaces which have to be defined by the user. Some popular spaces from literature are readily available as tuning spaces.

Example Usage

Tune the hyperparameters of a classification tree on the Palmer Penguins data set with random search.

library(mlr3verse)

# retrieve task
task = tsk("penguins")

# load learner and set search space
learner = lrn("classif.rpart",
  cp = to_tune(1e-04, 1e-1, logscale = TRUE),
  minsplit = to_tune(2, 128, logscale = TRUE)
)

# load tuner and set batch size
tuner = tnr("random_search", batch_size = 10)

# hyperparameter tuning on the palmer penguins data set
instance = tune(
  tuner = tuner,
  task = task,
  learner = learner,
  resampling = rsmp("holdout"),
  measure = msr("classif.ce"),
  term_evals = 50
)

# best performing hyperparameter configuration
instance$result

          cp  minsplit learner_param_vals  x_domain classif.ce
       <num>     <num>             <list>    <list>      <num>
1: -4.959292 0.9012323          <list[3]> <list[2]> 0.02608696

# surface plot
autoplot(instance, type = "surface")

# fit final model on complete data set
learner$param_set$values = instance$result_learner_param_vals
learner$train(task)

print(learner)

<LearnerClassifRpart:classif.rpart>: Classification Tree
* Model: rpart
* Parameters: cp=0.007018, minsplit=2, xval=0
* Packages: mlr3, rpart
* Predict Types:  [response], prob
* Feature Types: logical, integer, numeric, factor, ordered
* Properties: importance, missings, multiclass, selected_features,
  twoclass, weights