Error with SVM hyperparameter tuning in mlrMBO Bayesian optimization

Question

I am trying to optimize an SVM for a classification task, which has worked for many other models I've tried this process on. Yet, when I used an SVM in my model based optimization function it returns an error: "Error in checkStuff(fun, design, learner, control): Provided learner does not support factor parameters."

Attached is the relevant code. In my training task, all independent variables are numeric, the only factor is my outcome of interest.

library(mlr)
library(mlrMBO)
library(dplyr)
library(PRROC)
library(ggplot2)
library(DiceKriging)
traindf <- read.csv("/Users/njr/Google Drive/HMS IR Research/NSQIP Research/Endovascular/randomtraining.csv")
testdf <- read.csv("/Users/njr/Google Drive/HMS IR Research/NSQIP Research/Endovascular/randomtesting.csv")
traindf$Amputation<-as.factor(traindf$Amputation)
testdf$Amputation <- as.factor(testdf$Amputation)
trn.task = makeClassifTask(data = traindf, target = "Amputation", positive = "2")
test.task = makeClassifTask(data = testdf, target = "Amputation", positive = "2")
set.seed(9)
svmlrn =  makeLearner("classif.svm", predict.type = "prob")

svm_model <- mlr::train(svmlrn, task = trn.task)
res = makeResampleDesc("CV", iters = 10, stratify = TRUE)
par5 = makeParamSet(
  makeDiscreteParam("kernel", values = c("radial", "polynomial", "linear")),
  makeNumericParam("cost", -15, 15, trafo = function(x) 2^x),
  makeNumericParam("gamma", -15, 15, trafo = function(x) 2^x, requires = quote(kernel == "radial")),
  makeIntegerParam("degree", lower = 1, upper = 4, requires = quote(kernel == "polynomial"))
)
mbo.ctrl = makeMBOControl()
mbo.ctrl = setMBOControlInfill(mbo.ctrl, crit = crit.ei)
mbo.ctrl = setMBOControlTermination(mbo.ctrl, iters = 35, max.evals = 25)
design.mat = generateRandomDesign(n = 50, par.set = par5)
surrogate.lrn = makeLearner("regr.km", predict.type = "se")
ctrl = mlr::makeTuneControlMBO(learner = surrogate.lrn, mbo.control = mbo.ctrl, mbo.design = design.mat)

parallelStartMulticore(cpus = 8L)
res.mbo = tuneParams(makeLearner("classif.svm"), trn.task, resampling = res, par.set = par5, control = ctrl, 
                     show.info = TRUE, measures = auc)
parallelStop()

this is the traceback error code:

6.
stop("Provided learner does not support factor parameters.")
5.
checkStuff(fun, design, learner, control)
4.
initOptProblem(fun = fun, design = design, learner = learner, control = control, show.info = show.info, more.args = more.args)
3.
mlrMBO::mbo(tff, design = control$mbo.design, learner = control$learner, control = mbo.control, show.info = FALSE)
2.
sel.func(learner, task, resampling, measures, par.set, control, opt.path, show.info, resample.fun)
1.
tuneParams(makeLearner("classif.svm"), trn.task, resampling = res, par.set = par5, control = ctrl, show.info = TRUE, measures = auc)

Answer 1

The problem is that your parameter set has a categorical parameter (kernel) and the surrogate model you're using (regr.km) doesn't support that. You could try for example a random forest as surrogate model instead.