Check for "/" in feature names (#660)

lerobot/common/datasets/lerobot_dataset.py

@@ -304,6 +304,13 @@ class LeRobotDatasetMetadata:
             )
         else:
             # TODO(aliberts, rcadene): implement sanity check for features
+
+            # check if none of the features contains a "/" in their names,
+            # as this would break the dict flattening in the stats computation, which uses '/' as separator
+            for key in features:
+                if "/" in key:
+                    raise ValueError(f"Feature names should not contain '/'. Found '/' in feature '{key}'.")
+
             features = {**features, **DEFAULT_FEATURES}
 
         obj.tasks, obj.stats, obj.episodes = {}, {}, []

tests/test_datasets.py

@@ -414,3 +414,20 @@ def test_create_branch():
 
     # Clean
     api.delete_repo(repo_id, repo_type=repo_type)
+
+
+def test_dataset_feature_with_forward_slash_raises_error():
+    # make sure dir does not exist
+    from lerobot.common.datasets.lerobot_dataset import LEROBOT_HOME
+
+    dataset_dir = LEROBOT_HOME / "lerobot/test/with/slash"
+    # make sure does not exist
+    if dataset_dir.exists():
+        dataset_dir.rmdir()
+
+    with pytest.raises(ValueError):
+        LeRobotDataset.create(
+            repo_id="lerobot/test/with/slash",
+            fps=30,
+            features={"a/b": {"dtype": "float32", "shape": 2, "names": None}},
+        )