I am trying to generate three separate torch data sets from the torch Dataset class but I am not sure how to do it or if it is possible, owing to __getitem__'s functionality. I would like to have separate torch data sets that I can then pass into data loaders on their own. Can I return 3 separate torch data sets from this class or do I need to make a class for each train, dev, and test set file?
Below is an example:
import torch
from torch.utils.data import DataLoader, Dataset
import pytreebank
import torchtext as tt
from torchtext import datasets
import pandas as pd
# prepare torch data set
class SST5DataSet(torch.utils.data.Dataset):
    '''
    This prepares the official Stanford Sentiment Treebank
    (https://nlp.stanford.edu/~socherr/EMNLP2013_RNTN.pdf) for traininig
    in PyTorch.
    '''
    def __init__(self, is_finegrained=True, transform=None):
        # initialize flag; set false for binary classification
        self.is_finegrained = is_finegrained
        # binary categories: 1 and 3 only
        self.binary = [1, 3]
        # download sst if necessary
        tt.datasets.SST.download(root='.data')
        # load sst
        dataset = pytreebank.load_sst('.data\\sst\\trees')
        # prase train test dev
        for category in ['train', 'test', 'dev']:
            with open('.data\\sst\\trees\\sst_{}.txt'.format(category), 'w') as outfile:
                for item in dataset[category]:
                    outfile.write("{}\t{}\n".format(
                        item.to_labeled_lines()[0][0],
                        item.to_labeled_lines()[0][1]))
        # initialize train, test dev
        self.train = pd.read_csv('.data\\sst\\trees\\sst_train.txt', sep='\t',
                                 header=None, names=['label', 'text'],
                                 encoding='latin-1')
        self.dev = pd.read_csv('.data\\sst\\trees\\sst_dev.txt', sep='\t',
                               header=None, names=['label', 'text'],
                               encoding='latin-1')
        self.test = pd.read_csv('.data\\sst\\trees\\sst_test.txt', sep='\t',
                                header=None, names=['label', 'text'],
                                encoding='latin-1')

        # filter if fine_grained
        if self.is_finegrained is False:
            self.train = self.train.loc[self.train['label'].isin(self.binary)].reset_index(drop=True)
            self.dev = self.dev.loc[self.dev['label'].isin(self.binary)].reset_index(drop=True)
            self.test = self.test.loc[self.test['label'].isin(self.binary)].reset_index(drop=True)

            # map to 0, 1
            self.train['label'] = self.train['label'].map({1: 0, 3: 1})
            self.dev['label'] = self.dev['label'].map({1: 0, 3: 1})
            self.test['label'] = self.test['label'].map({1: 0, 3: 1})

        # initialize the transform if specified
        self.transform = transform

    # get len
    def __len__(self):
        return self.train.shape[0], self.dev.shape[0], self.test.shape[0]

    # pull a sample of data
    def __getitem__(self, idx):
        if torch.is_tensor(idx):
            idx = idx.tolist()

        # return train, dev, test
        train = {'text': self.train.text[idx],
                  'label': self.train.label[idx],
                  'idx': idx}

        dev = {'text': self.dev.text[idx],
                  'label': self.dev.label[idx],
                  'idx': idx}

        test = {'text': self.test.text[idx],
                  'label': self.test.label[idx],
                  'idx': idx}

        return train, dev, test

# concats them all together
out = SST5DataSet(is_finegrained=False)

# check data
for i, batch in enumerate(out):
    if i == 0:
        break

batch