Towards a Unified Benchmark for Reinforcement Learning in Sparse Reward Environments

Reinforcement learning in sparse reward environments is challenging and has recently received increasing attention, with dozens of new algorithms proposed every year. Despite promising results demonstrated in various sparse reward environments, this domain lacks a unified definition of a sparse reward environment and an experimentally fair way to compare existing algorithms. These issues significantly affect the in-depth analysis of the underlying problem and hinder further studies. This paper proposes a benchmark to unify the selection of environments and the comparison of algorithms. We first define sparsity to describe the proportion of rewarded states in the entire state space and select environments by this sparsity. Inspired by the sparsity concept, we categorize the existing algorithms into two classes. To provide a fair comparison of different algorithms, we propose a new metric along with a standard protocol for performance evaluation. Primary experimental evaluations of seven algorithms in ten environments provide a startup user guide of the proposed benchmark. We hope the proposed benchmark will promote the research of reinforcement learning algorithms in sparse reward environments. The source code of this work is published on https://github.com/simayuhe/ICONIP_Benchmark.git .