Coverage-based Example Selection for In-Context Learning

In-context learning (ICL), the ability of large language models to perform novel tasks by conditioning on a prompt with a few task examples, requires demonstrations that are informative about the test instance. The standard approach of independently selecting the most similar examples selects redundant demonstrations while overlooking important information. This work proposes a framework for assessing the informativeness of demonstrations based on their coverage of salient aspects (e.g., reasoning patterns) of the test input. Using this framework, we show that contextual token embeddings effectively capture these salient aspects, and their recall measured using BERTScore-Recall (BSR) yields a reliable measure of informativeness. Further, we extend recall metrics like BSR to propose their set versions to find maximally informative sets of demonstrations. On 6 complex compositional generation tasks and 7 diverse LLMs, we show that Set-BSR outperforms the standard similarity-based approach by up to 16% on average and, despite being learning-free, often surpasses methods that leverage task or LLM-specific training.