# Re-Pair Compression of Inverted Lists

## TL;DR

This paper explores using Re-Pair compression for inverted lists, offering a novel approach that balances speed and space, but still needs improvements to surpass current methods.

## Contribution

It introduces Re-Pair based compression variants for inverted lists and evaluates their performance, providing a new direction for efficient list intersection.

## Key findings

- Re-Pair variants offer a promising time/space tradeoff
- Current methods still outperform Re-Pair variants in some aspects
- Further improvements are needed for Re-Pair to surpass state-of-the-art techniques

## Abstract

Compression of inverted lists with methods that support fast intersection operations is an active research topic. Most compression schemes rely on encoding differences between consecutive positions with techniques that favor small numbers. In this paper we explore a completely different alternative: We use Re-Pair compression of those differences. While Re-Pair by itself offers fast decompression at arbitrary positions in main and secondary memory, we introduce variants that in addition speed up the operations required for inverted list intersection. We compare the resulting data structures with several recent proposals under various list intersection algorithms, to conclude that our Re-Pair variants offer an interesting time/space tradeoff for this problem, yet further improvements are required for it to improve upon the state of the art.