fix #296

Former-commit-id: 69e9ed9b96a7cfb3d3b43ec5ddd01aa0bfd9b784

src/llmtuner/dsets/loader.py

@@ -2,7 +2,7 @@ import os
 import hashlib
 from typing import TYPE_CHECKING, List, Optional
 
-from datasets import concatenate_datasets, interleave_datasets, load_dataset
+from datasets import Value, concatenate_datasets, interleave_datasets, load_dataset
 
 from llmtuner.extras.logging import get_logger
 
@@ -93,7 +93,11 @@ def get_dataset(
                 dataset = dataset.rename_column(getattr(dataset_attr, column_name), column_name)
 
         if dataset_attr.source_prefix: # add prefix
-            dataset = dataset.map(lambda _: {"prefix": dataset_attr.source_prefix})
+            features = None
+            if data_args.streaming:
+                features = dataset.features
+                features["prefix"] = Value(dtype="string", id=None)
+            dataset = dataset.map(lambda _: {"prefix": dataset_attr.source_prefix}, features=features)
 
         all_datasets.append(dataset)