add automatic detection of the progress path

docs/source/sarm.mdx

@@ -465,14 +465,13 @@ This script:
 
 ### Step 5b: Train Policy with RA-BC
 
-Once you have the progress file, train your policy with RA-BC weighting. Currently PI0, PI0.5 and SmolVLA are supported with RA-BC:
+Once you have the progress file, train your policy with RA-BC weighting. The progress file is auto-detected from the dataset path (`sarm_progress.parquet`) if not explicitly provided. Currently PI0, PI0.5 and SmolVLA are supported with RA-BC:
 
 ```bash
 python src/lerobot/scripts/lerobot_train.py \
   --dataset.repo_id=your-username/your-dataset \
   --policy.type=pi0 \
   --sample_weighting.type=rabc \
-  --sample_weighting.progress_path=path/to/sarm_progress.parquet \
   --sample_weighting.head_mode=sparse \
   --sample_weighting.kappa=0.01 \
   --output_dir=outputs/train/policy_rabc \
@@ -489,13 +488,13 @@ The training script automatically:
 
 **RA-BC Arguments:**
 
-| Argument                            | Description                                            | Default   |
-| ----------------------------------- | ------------------------------------------------------ | --------- |
-| `--sample_weighting.type`           | Weighting strategy type (`rabc` or `uniform`)          | `rabc`    |
-| `--sample_weighting.progress_path`  | Path to progress parquet file (required for RABC)      | (required)|
-| `--sample_weighting.head_mode`      | Which SARM head's progress to use: `sparse` or `dense` | `sparse`  |
-| `--sample_weighting.kappa`          | Threshold κ for high-quality samples                   | `0.01`    |
-| `--sample_weighting.epsilon`        | Small constant for numerical stability                 | `1e-6`    |
+| Argument                           | Description                                            | Default                 |
+| ---------------------------------- | ------------------------------------------------------ | ----------------------- |
+| `--sample_weighting.type`          | Weighting strategy type (`rabc` or `uniform`)          | `rabc`                  |
+| `--sample_weighting.progress_path` | Path to progress parquet file                          | `sarm_progress.parquet` |
+| `--sample_weighting.head_mode`     | Which SARM head's progress to use: `sparse` or `dense` | `sparse`                |
+| `--sample_weighting.kappa`         | Threshold κ for high-quality samples                   | `0.01`                  |
+| `--sample_weighting.epsilon`       | Small constant for numerical stability                 | `1e-6`                  |
 
 ### Tuning RA-BC Kappa
 
@@ -513,11 +512,11 @@ The `kappa` parameter is the threshold that determines which samples get full we
 
 Monitor these WandB metrics during training:
 
-| Metric                          | Healthy Range | Problem Indicator         |
-| ------------------------------- | ------------- | ------------------------- |
-| `sample_weight_mean_weight`     | 0.3 - 0.8     | ≈ 1.0 means kappa too low |
-| `sample_weighting/delta_mean`   | > 0           | Should be positive        |
-| `sample_weighting/delta_std`    | > 0           | Variance in data quality  |
+| Metric                        | Healthy Range | Problem Indicator         |
+| ----------------------------- | ------------- | ------------------------- |
+| `sample_weight_mean_weight`   | 0.3 - 0.8     | ≈ 1.0 means kappa too low |
+| `sample_weighting/delta_mean` | > 0           | Should be positive        |
+| `sample_weighting/delta_std`  | > 0           | Variance in data quality  |
 
 **If `sample_weight_mean_weight ≈ 1.0`:** Your kappa is too low. Most samples have `delta > kappa` and bypass the soft-weighting entirely. RA-BC becomes equivalent to vanilla BC.
 
@@ -553,7 +552,6 @@ accelerate launch \
   --dataset.repo_id=your-username/your-dataset \
   --policy.type=pi0 \
   --sample_weighting.type=rabc \
-  --sample_weighting.progress_path=path/to/sarm_progress.parquet \
   --sample_weighting.kappa=0.01 \
   --output_dir=outputs/train/policy_rabc \
   --batch_size=32 \

src/lerobot/scripts/lerobot_train.py

@@ -382,7 +382,13 @@ def train(cfg: TrainPipelineConfig, accelerator: Accelerator | None = None):
 
         if is_main_process:
             logging.info(f"Creating sample weighter: {cfg.sample_weighting.type}")
-        sample_weighter = make_sample_weighter(cfg.sample_weighting, policy, device)
+        sample_weighter = make_sample_weighter(
+            cfg.sample_weighting,
+            policy,
+            device,
+            dataset_root=cfg.dataset.root,
+            dataset_repo_id=cfg.dataset.repo_id,
+        )
 
     step = 0  # number of policy updates (forward + backward + optim)
 

src/lerobot/utils/sample_weighting.py

@@ -28,7 +28,7 @@ Example usage:
         kappa: 0.01
 
     # In training script
-    sample_weighter = make_sample_weighter(cfg.sample_weighting, policy, device)
+    sample_weighter = make_sample_weighter(cfg.sample_weighting, policy, device, dataset_root=cfg.dataset.root, dataset_repo_id=cfg.dataset.repo_id)
     ...
     weights, stats = sample_weighter.compute_batch_weights(batch)
 """
@@ -37,6 +37,7 @@ from __future__ import annotations
 
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, field
+from pathlib import Path
 from typing import TYPE_CHECKING
 
 import torch
@@ -63,21 +64,12 @@ class SampleWeighter(ABC):
         Args:
             batch: Training batch dictionary containing at minimum an "index" key
                    with global frame indices.
-
-        Returns:
-            Tuple of:
-            - weights: Tensor of shape (batch_size,) with per-sample weights,
-                      normalized to sum to batch_size for stable gradients.
-            - stats: Dictionary with logging-friendly statistics about the weights.
         """
 
     @abstractmethod
     def get_stats(self) -> dict:
         """
         Get global statistics about the weighting strategy.
-
-        Returns:
-            Dictionary with statistics for logging (e.g., mean delta, coverage).
         """
 
 
@@ -112,6 +104,8 @@ def make_sample_weighter(
     config: SampleWeightingConfig | None,
     policy: PreTrainedPolicy,
     device: torch.device,
+    dataset_root: str | None = None,
+    dataset_repo_id: str | None = None,
 ) -> SampleWeighter | None:
     """
     Factory function to create a SampleWeighter from config.
@@ -122,18 +116,14 @@ def make_sample_weighter(
         config: Sample weighting configuration, or None to disable weighting.
         policy: The policy being trained (used to extract chunk_size, etc.)
         device: Device to place weight tensors on.
-
-    Returns:
-        SampleWeighter instance, or None if config is None.
-
-    Raises:
-        ValueError: If the weighting type is unknown or required params are missing.
+        dataset_root: Local path to dataset root (for auto-detecting progress_path).
+        dataset_repo_id: HuggingFace repo ID (for auto-detecting progress_path).
     """
     if config is None:
         return None
 
     if config.type == "rabc":
-        return _make_rabc_weighter(config, policy, device)
+        return _make_rabc_weighter(config, policy, device, dataset_root, dataset_repo_id)
 
     if config.type == "uniform":
         # No-op weighter that returns uniform weights
@@ -146,8 +136,18 @@ def _make_rabc_weighter(
     config: SampleWeightingConfig,
     policy: PreTrainedPolicy,
     device: torch.device,
+    dataset_root: str | None = None,
+    dataset_repo_id: str | None = None,
 ) -> SampleWeighter:
-    """Create RABC weighter with policy-specific initialization."""
+    """Create RABC weighter with policy-specific initialization.
+
+    Args:
+        config: Sample weighting configuration.
+        policy: The policy being trained (used to extract chunk_size).
+        device: Device to place weight tensors on.
+        dataset_root: Local path to dataset root (for auto-detecting progress_path).
+        dataset_repo_id: HuggingFace repo ID (for auto-detecting progress_path).
+    """
     # Import here to avoid circular imports and keep RABC code in SARM module
     from lerobot.policies.sarm.rabc import RABCWeights
 
@@ -159,15 +159,23 @@ def _make_rabc_weighter(
             "This is typically set for action-chunking policies like ACT, Diffusion, PI0, etc."
         )
 
-    if config.progress_path is None:
-        raise ValueError(
-            "RABC sample weighting requires 'progress_path' to be set. "
-            "Generate progress values using: "
-            "python -m lerobot.policies.sarm.compute_rabc_weights --help"
-        )
+    # Determine progress_path: use explicit config or auto-detect from dataset
+    progress_path = config.progress_path
+    if progress_path is None:
+        if dataset_root:
+            progress_path = str(Path(dataset_root) / "sarm_progress.parquet")
+        elif dataset_repo_id:
+            progress_path = f"hf://datasets/{dataset_repo_id}/sarm_progress.parquet"
+        else:
+            raise ValueError(
+                "RABC sample weighting requires 'progress_path' to be set, "
+                "or dataset_root/dataset_repo_id for auto-detection. "
+                "Generate progress values using: "
+                "python -m lerobot.policies.sarm.compute_rabc_weights --help"
+            )
 
     return RABCWeights(
-        progress_path=config.progress_path,
+        progress_path=progress_path,
         chunk_size=chunk_size,
         head_mode=config.head_mode,
         kappa=config.kappa,
@@ -209,12 +217,6 @@ class UniformWeighter(SampleWeighter):
 
         Args:
             batch: Training batch dictionary.
-
-        Returns:
-            Batch size, or 1 if it cannot be determined.
-
-        Raises:
-            ValueError: If batch is empty.
         """
         if not batch:
             raise ValueError("Cannot determine batch size from empty batch")

tests/utils/test_sample_weighting.py

@@ -231,8 +231,8 @@ def test_factory_rabc_requires_chunk_size():
         make_sample_weighter(config, policy, device)
 
 
-def test_factory_rabc_requires_progress_path():
-    """Test that RABC weighter requires progress_path."""
+def test_factory_rabc_requires_progress_path_or_dataset_info():
+    """Test that RABC weighter requires progress_path or dataset info for auto-detection."""
     config = SampleWeightingConfig(
         type="rabc",
         progress_path=None,  # No progress path
@@ -242,10 +242,63 @@ def test_factory_rabc_requires_progress_path():
     policy.config.chunk_size = 50
     device = torch.device("cpu")
 
+    # Should fail when no progress_path AND no dataset info
     with pytest.raises(ValueError, match="progress_path"):
         make_sample_weighter(config, policy, device)
 
 
+def test_factory_rabc_auto_detects_from_dataset_root(sample_progress_parquet):
+    """Test that RABC weighter auto-detects progress_path from dataset_root."""
+    config = SampleWeightingConfig(
+        type="rabc",
+        progress_path=None,  # Not provided, should auto-detect
+    )
+    policy = Mock()
+    policy.config = Mock()
+    policy.config.chunk_size = 5
+    device = torch.device("cpu")
+
+    # The parquet file is at sample_progress_parquet, get its parent directory
+    dataset_root = sample_progress_parquet.parent
+    weighter = make_sample_weighter(
+        config,
+        policy,
+        device,
+        dataset_root=str(dataset_root),
+    )
+
+    assert weighter is not None
+    from lerobot.policies.sarm.rabc import RABCWeights
+
+    assert isinstance(weighter, RABCWeights)
+
+
+def test_factory_rabc_auto_detects_from_repo_id():
+    """Test that RABC weighter constructs HF path from repo_id."""
+    config = SampleWeightingConfig(
+        type="rabc",
+        progress_path=None,  # Not provided, should auto-detect
+    )
+    policy = Mock()
+    policy.config = Mock()
+    policy.config.chunk_size = 50
+    device = torch.device("cpu")
+
+    # This will construct the path but fail when trying to load (file doesn't exist)
+    # We just verify it doesn't raise the "progress_path required" error
+    with pytest.raises(Exception) as exc_info:
+        make_sample_weighter(
+            config,
+            policy,
+            device,
+            dataset_repo_id="test-user/test-dataset",
+        )
+    # Should NOT be the "progress_path required" error - it should try to load the file
+    assert (
+        "progress_path" not in str(exc_info.value).lower() or "auto-detection" in str(exc_info.value).lower()
+    )
+
+
 # =============================================================================
 # Integration Tests with RABCWeights
 # =============================================================================