QC-Forest: a Classical-Quantum Algorithm to Provably Speedup Retraining of Random Forest

TL;DR

QC-Forest introduces a classical-quantum algorithm that significantly accelerates the retraining of Random Forest models in data streams, maintaining accuracy while reducing runtime complexity from linear to poly-logarithmic.

Contribution

The paper presents QC-Forest, a novel quantum-enhanced algorithm that speeds up RF retraining in streaming data scenarios, expanding quantum methods to multi-class problems and replacing quantum subroutines with classical ones.

Findings

Achieves poly-logarithmic runtime in the number of samples.

Maintains competitive accuracy compared to classical RF methods.

Demonstrates significant speedup on benchmark datasets with up to 80,000 samples.

Abstract

Random Forest (RF) is a popular tree-ensemble method for supervised learning, prized for its ease of use and flexibility. Online RF models require to account for new training data to maintain model accuracy. This is particularly important in applications where data is periodically and sequentially generated over time in data streams, such as auto-driving systems, and credit card payments. In this setting, performing periodic model retraining with the old and new data accumulated is beneficial as it fully captures possible drifts in the data distribution over time. However, this is unpractical with state-of-the-art classical algorithms for RF as they scale linearly with the accumulated number of samples. We propose QC-Forest, a classical-quantum algorithm designed to time-efficiently retrain RF models in the streaming setting for multi-class classification and regression, achieving a runtime poly-logarithmic in the total number of accumulated samples. QC-Forest leverages Des-q, a quantum algorithm for single tree construction and retraining proposed by Kumar et al. by expanding to multi-class classification, as the original proposal was limited to binary classes, and introducing an exact classical method to replace an underlying quantum subroutine incurring a finite error, while maintaining the same poly-logarithmic dependence. Finally, we showcase that QC-Forest achieves competitive accuracy in comparison to state-of-the-art RF methods on widely used benchmark datasets with up to 80,000 samples, while significantly speeding up the model retrain.