title: Pytorch DataLoader multiple data source
body: <p>I am trying to use Pytorch dataloader to define my own dataset, but I am not sure how to load multiple data source:</p>
  
  <p>My current code:</p>
  
  <pre><code>class MultipleSourceDataSet(Dataset):
      def __init__ (self, json_file, root_dir, transform = None):
          with open(root_dir + 'block0.json') as f:
              self.result = torch.Tensor(json.load(f))
  
      self.root_dir = root_dir
      self.transform = transform
  
      def __len__(self):
          return len(self.result[0])
  
      def __getitem__ (self):
          None
  </code></pre>
  
  <p>The data source is 50 blocks under <code>root_dir = ~/Documents/blocks/</code></p>
  
  <p>I split them and avoid to combine them directly before since this is a very big dataset.</p>
  
  <p>How can I load them into a single dataloader? </p>