uniformly use skip for both (map-style) Dataset and IterableDataset

ghstack-source-id: d82c233f21dddc74794d9c492a781dffc52eb5de
Pull Request resolved: #521

torchtitan/datasets/hf_datasets.py

@@ -11,18 +11,12 @@
 from torch.distributed.checkpoint.stateful import Stateful
 from torch.utils.data import IterableDataset
 
-try:
-    from torchdata.stateful_dataloader import StatefulDataLoader
-except ImportError as e:
-    raise ImportError(
-        "Please install the latest torchdata nightly to use StatefulDataloader via:"
-        "pip3 install --pre torchdata --index-url https://download.pytorch.org/whl/nightly"
-    ) from e
+from torchdata.stateful_dataloader import StatefulDataLoader
 
 from torchtitan.datasets.tokenizer import Tokenizer
 from torchtitan.logging import logger
 
-from datasets import load_dataset
+from datasets import Dataset, load_dataset
 from datasets.distributed import split_dataset_by_node
 
 # map from dataset name to a local directory, or
@@ -102,7 +96,7 @@ def __init__(
         else:
             ds = load_dataset(dataset_path, split="train")
 
-        # TODO: support shuffling and checkpointing
+        # TODO: support shuffling
         self.dataset_name = dataset_name
         self._data = split_dataset_by_node(ds, rank, world_size)
         self._tokenizer = tokenizer
@@ -143,17 +137,10 @@ def _get_data_iter(self):
         if self._sample_idx == 0:
             return iter(self._data)
 
-        # Skip samples
-        if isinstance(self._data, IterableDataset):
-            it = iter(self._data)
-            # Naively iterate through the samples as skip may not be supported
-            for _ in range(self._sample_idx):
-                next(it)
-            return it
-
         # As skipping to the end throws an error in case of map-style dataset, return an empty iterator
-        if self._sample_idx == len(self._data):
+        if isinstance(self._data, Dataset) and self._sample_idx == len(self._data):
             return iter([])
+
         return iter(self._data.skip(self._sample_idx))
 
     def load_state_dict(self, state_dict):
@@ -179,7 +166,7 @@ def state_dict(self) -> Dict[str, Any]:
         return {self._rank_id: pickle.dumps(super().state_dict())}
 
     def load_state_dict(self, state_dict: Dict[str, Any]) -> None:
-        # State being empty is valid, don't log a warning
+        # State being empty is valid
         if not state_dict:
             return