问题
To publish reproducible results obtained in the mlr package one should use the set.seed() function to control the randomness of the code.
Testing, it seems such practice doesn't lead to the desired results, in which different runs of the code give slightly different outputs, such as reported in the source of this question and following code.
Here's some reproducible code
## libraries
library(mlr)
library(parallel)
library(parallelMap)
## options
set.seed(1)
cv.n <- 3
bag.n <- 3
## data
dataset <- data.frame(matrix(rnorm(15000), ncol=5))
dataset$target <- factor(c(rep(0, 1500), rep(1, 1500)))
## task
classif.task <- makeClassifTask(id="dataset", data=dataset, target="target", positive="1")
## resampling strategy
rdesc <- makeResampleDesc("CV", iters=cv.n)
## number of features and observations
nf <- getTaskNFeats(classif.task)
no <- getTaskSize(classif.task)
# training and test set
train.set <- sample(no, size = round(0.8*no))
test.set <- setdiff(seq(no), train.set)
## learners
# decision tree
dt.lrn <- makeLearner("classif.rpart")
dt.lrn <- setPredictType(dt.lrn, predict.type="prob")
# random forest
rf.lrn <- makeLearner("classif.randomForest")
rf.lrn <- setPredictType(rf.lrn, predict.type="prob")
# neural network
nn.lrn <- makeLearner("classif.nnet", MaxNWts=5000, trace=FALSE)
nn.lrn <- makeBaggingWrapper(nn.lrn, bw.iters=bag.n)
nn.lrn <- setPredictType(nn.lrn, predict.type="prob")
# support vector machine
svm.lrn <- makeLearner("classif.svm", kernel="radial")
svm.lrn <- makeBaggingWrapper(svm.lrn, bw.iters=bag.n)
svm.lrn <- setPredictType(svm.lrn, predict.type="prob")
# gradient boosting machine
gbm.lrn <- makeLearner("classif.gbm", distribution="adaboost")
gbm.lrn <- makeBaggingWrapper(gbm.lrn, bw.iters=bag.n)
gbm.lrn <- setPredictType(gbm.lrn, predict.type="prob")
## benchmark
lrns <- list(dt.lrn, rf.lrn, nn.lrn, svm.lrn, gbm.lrn)
parallelStartMulticore(detectCores(), level="mlr.resample")
for (i in 1:5) {
bmrk <- suppressMessages(benchmark(lrns, subsetTask(classif.task, subset=train.set), rdesc, measures=list(mmce, acc, auc, tpr, tnr, ppv, f1)))
print(bmrk)
}
parallelStop()
And here's the result:
task.id learner.id mmce.test.mean acc.test.mean auc.test.mean tpr.test.mean tnr.test.mean ppv.test.mean f1.test.mean
1 dataset classif.rpart 0.5050000 0.4950000 0.5035564 0.5857604 0.4216936 0.5001443 0.5132852
2 dataset classif.randomForest 0.5141667 0.4858333 0.4835233 0.4811167 0.4913591 0.4813667 0.4805184
3 dataset classif.nnet.bagged 0.4841667 0.5158333 0.5130378 0.5134648 0.5132865 0.5065907 0.5053251
4 dataset classif.svm.bagged 0.5200000 0.4800000 0.4783791 0.4596055 0.5038720 0.4754137 0.4634932
5 dataset classif.gbm.bagged 0.5175000 0.4825000 0.4999211 0.5681540 0.4307022 NaN 0.4079824
task.id learner.id mmce.test.mean acc.test.mean auc.test.mean tpr.test.mean tnr.test.mean ppv.test.mean f1.test.mean
1 dataset classif.rpart 0.5095833 0.4904167 0.4887304 0.5896894 0.3914619 0.4875778 0.5309759
2 dataset classif.randomForest 0.4920833 0.5079167 0.5094901 0.4981170 0.5180616 0.5037475 0.5005092
3 dataset classif.nnet.bagged 0.5037500 0.4962500 0.5007292 0.5182091 0.4794809 0.4894119 0.4873004
4 dataset classif.svm.bagged 0.4870833 0.5129167 0.5243128 0.4687382 0.5571168 0.5102900 0.4867651
5 dataset classif.gbm.bagged 0.5041667 0.4958333 0.5037020 0.3307626 0.6699108 NaN 0.2177101
task.id learner.id mmce.test.mean acc.test.mean auc.test.mean tpr.test.mean tnr.test.mean ppv.test.mean f1.test.mean
1 dataset classif.rpart 0.5154167 0.4845833 0.4997415 0.6023993 0.3909165 NaN 0.4194502
2 dataset classif.randomForest 0.5058333 0.4941667 0.5092414 0.4792270 0.5101295 0.4898916 0.4837489
3 dataset classif.nnet.bagged 0.4900000 0.5100000 0.5113847 0.6091273 0.4093971 0.5044188 0.5500985
4 dataset classif.svm.bagged 0.5025000 0.4975000 0.5093498 0.4597310 0.5386824 0.4937899 0.4711354
5 dataset classif.gbm.bagged 0.5045833 0.4954167 0.4966777 0.3333333 0.6666667 NaN 0.2181105
task.id learner.id mmce.test.mean acc.test.mean auc.test.mean tpr.test.mean tnr.test.mean ppv.test.mean f1.test.mean
1 dataset classif.rpart 0.5116667 0.4883333 0.4816318 0.40531599 0.5665951 0.4699498 0.42524328
2 dataset classif.randomForest 0.4966667 0.5033333 0.5088898 0.48810185 0.5189027 0.4994051 0.49328978
3 dataset classif.nnet.bagged 0.5229167 0.4770833 0.4914172 0.35887024 0.5964164 0.4683719 0.40099597
4 dataset classif.svm.bagged 0.5016667 0.4983333 0.4926987 0.49163773 0.5047228 0.4935696 0.49220550
5 dataset classif.gbm.bagged 0.5016667 0.4983333 0.4918831 0.04242424 0.9485944 NaN 0.06559572
task.id learner.id mmce.test.mean acc.test.mean auc.test.mean tpr.test.mean tnr.test.mean ppv.test.mean f1.test.mean
1 dataset classif.rpart 0.5016667 0.4983333 0.4928826 0.4982873 0.4894108 0.4845022 0.4687902
2 dataset classif.randomForest 0.5050000 0.4950000 0.4945688 0.4973200 0.4935429 0.4909559 0.4936415
3 dataset classif.nnet.bagged 0.5137500 0.4862500 0.4818591 0.4314678 0.5387981 0.4780440 0.4533055
4 dataset classif.svm.bagged 0.5054167 0.4945833 0.4962764 0.5692158 0.4246046 0.4932935 0.5251290
5 dataset classif.gbm.bagged 0.5129167 0.4870833 0.4852225 0.2393787 0.7450389 NaN 0.1945371
You can see different runs give different numerical outputs. And this is true among every classifier, from the most stochastic ones to the least.
What can I do to ensure reproducible results?
回答1:
As pointed in this comment, the code above is run with parallelization. To ensure the reproducibility in every parallel run one should use set.seed(123, "L'Ecuyer"), if you don't use Windows1.
1. Windows doesn't support forks, which are used in this multicore case for the parallel library.
来源：https://stackoverflow.com/questions/37843246/why-does-mlr-give-different-results-in-different-runs-even-when-using-set-seed