How to convert  torch.utils.data.Dataset to datasets.arrow_dataset.Dataset?
Hi,
I use torch.utils.data.Dataset to define my own data, but I need to use the 'map' function of datasets.arrow_dataset.Dataset later, so I hope to convert torch.utils.data.Dataset to datasets.arrow_dataset.Dataset.

Here is an example.
```
from torch.utils.data import Dataset
from datasets.arrow_dataset import Dataset as HFDataset

class ADataset(Dataset):
    def __init__(self, data): 
        super().__init__()
        self.data = data
    def __getitem__(self, index):
        return self.data[index]
    def __len__(self):
        return self.len
class MDataset():
    def __init__(self, tokenizer: AutoTokenizer, data_args, training_args):
        self.train_dataset = ADataset(data_args)
        self.tokenizer = tokenizer
        self.data_args = data_args

        self.train_dataset = self.train_dataset.map(
            self.process_function,
            batched=True,
            remove_columns=column_names,
            load_from_cache_file=True,
            desc="Running tokenizer on train dataset",
             )
    def process_function(self, examples):
        sentences = [" ".join(sample[0][3]) for sample in examples]

        tokenized = self.tokenizer(
            sentences,
            max_length=self.max_seq_len,
            padding=self.padding, 
            truncation=True)
```
But it would raise an ERROR, AttributeError: 'ADataset' object has no attribute 'map'.

so how to convert  torch.utils.data.Dataset to datasets.arrow_dataset.Dataset?

Thanks in advance!




