If you want to use validation data, you should set reference to training data
lgb.Dataset.set.reference(dataset, reference)object of class lgb.Dataset
object of class lgb.Dataset
the dataset you passed in
# \donttest{
setLGBMthreads(2L)
data.table::setDTthreads(1L)
# create training Dataset
data(agaricus.train, package ="lightgbm")
train <- agaricus.train
dtrain <- lgb.Dataset(train$data, label = train$label)
# create a validation Dataset, using dtrain as a reference
data(agaricus.test, package = "lightgbm")
test <- agaricus.test
dtest <- lgb.Dataset(test$data, label = test$label)
lgb.Dataset.set.reference(dtest, dtrain)
# }