Thanks for the link! But how can you use a custom dataset on that apporach?
They use a  dataset. In the official documentation they are using a single csv file for training: pd.read_csv(path/'cnndm_sample.csv'), but shouldn’t you use at least train and validation?
Edit:
The answer is:
dblock = DataBlock(blocks=blocks,                     get_x=ColReader('article'),                     get_y=ColReader('highlights'),                     splitter=RandomSplitter())
They split the single csv file into two dataloader object.