Reinforced Prompt Personalization for Recommendation with Large Language Models

Designing effective prompts can empower LLMs to understand user preferences and provide recommendations by leveraging LLMs' intent comprehension and knowledge utilization capabilities. However, existing research predominantly concentrates on task-wise prompting, developing fixed prompt templates composed of four patterns (i.e., role-playing, history records, reasoning guidance, and output format) and applying them to all users for a given task. Although convenient, task-wise prompting overlooks individual user differences, leading to potential mismatches in capturing user preferences. To address it, we introduce the concept of instance-wise prompting to personalize discrete prompts for individual users and propose Reinforced Prompt Personalization (RPP) to optimize the four patterns in prompts using multi-agent reinforcement learning (MARL). To boost efficiency, RPP formulates prompt personalization as selecting optimal sentences holistically across the four patterns, rather than optimizing word-by-word. To ensure the quality of prompts, RPP meticulously crafts diverse expressions for each of the four patterns, considering multiple analytical perspectives for specific recommendation tasks. In addition to RPP, our proposal of RPP+ aims to enhance the scalability of action space by dynamically refining actions with LLMs throughout the iterative process. We evaluate the effectiveness of RPP/RPP+ in ranking tasks over various datasets. Experimental results demonstrate the superiority of RPP/RPP+ over traditional recommender models, few-shot methods, and other prompt-based methods, underscoring the significance of instance-wise prompting for LLMs in recommendation tasks and validating the effectiveness of RPP/RPP+. Our code is available at https://github.com/maowenyu-11/RPP.