Towards Balanced Behavior Cloning from Imbalanced Datasets

TL;DR

This paper addresses the challenge of imbalanced datasets in robot imitation learning by analyzing the impact of data imbalance, proposing rebalancing algorithms, and introducing a meta-gradient approach to improve policy performance.

Contribution

The paper formally proves the effects of data imbalance on learned policies and introduces a novel meta-gradient rebalancing algorithm for better imitation learning.

Findings

Rebalancing datasets improves downstream policy performance.

Imbalanced data causes policies to favor the most frequent behaviors.

Meta-gradient rebalancing outperforms existing methods.

Abstract

Robots should be able to learn complex behaviors from human demonstrations. In practice, these human-provided datasets are inevitably imbalanced: i.e., the human demonstrates some subtasks more frequently than others. State-of-the-art methods default to treating each element of the human's dataset as equally important. So if -- for instance -- the majority of the human's data focuses on reaching a goal, and only a few state-action pairs move to avoid an obstacle, the learning algorithm will place greater emphasis on goal reaching. More generally, misalignment between the relative amounts of data and the importance of that data causes fundamental problems for imitation learning approaches. In this paper we analyze and develop learning methods that automatically account for mixed datasets. We formally prove that imbalanced data leads to imbalanced policies when each state-action pair is weighted equally; these policies emulate the most represented behaviors, and not the human's complex, multi-task demonstrations. We next explore algorithms that rebalance offline datasets (i.e., reweight the importance of different state-action pairs) without human oversight. Reweighting the dataset can enhance the overall policy performance. However, there is no free lunch: each method for autonomously rebalancing brings its own pros and cons. We formulate these advantages and disadvantages, helping other researchers identify when each type of approach is most appropriate. We conclude by introducing a novel meta-gradient rebalancing algorithm that addresses the primary limitations behind existing approaches. Our experiments show that dataset rebalancing leads to better downstream learning, improving the performance of general imitation learning algorithms without requiring additional data collection. See our project website: https://collab.me.vt.edu/data_curation/.