finish examples 2 and 3

lerobot/common/datasets/factory.py

@@ -21,7 +21,12 @@ def make_offline_buffer(
     overwrite_batch_size=None,
     overwrite_prefetch=None,
     stats_path=None,
+    # Don't actually load any data. This is a stand-in solution to get the transforms.
+    dummy=False,
 ):
+    if dummy and normalize and stats_path is None:
+        raise ValueError("`stats_path` is required if `dummy` and `normalize` are True.")
+
     if cfg.policy.balanced_sampling:
         assert cfg.online_steps > 0
         batch_size = None
@@ -93,6 +98,7 @@ def make_offline_buffer(
         root=DATA_DIR,
         pin_memory=pin_memory,
         prefetch=prefetch if isinstance(prefetch, int) else None,
+        dummy=dummy,
     )
 
     if cfg.policy.name == "tdmpc":