code: def __len__(self):
      return len(self.samples)
  
file_path: llama-recipes/src/llama_recipes/data/concatenator.py
imports: from tqdm import tqdm
  from itertools import chain
  from torch.utils.data import Dataset
label_desc: Use image node_id 3 for calling the ConcatDataset obj's underlying member method code with example usage: obj.__len__() and returns: len