OCTree: Using LLMs and Decision Tree Reasoning for Automated Feature Generation in Tabular Data

Основные понятия

OCTree is a novel framework that leverages large language models (LLMs) and decision tree reasoning to automate the generation of effective features for tabular data, improving the performance of various prediction models.

Аннотация

• Bibliographic Information: Nam, J., Kim, K., Oh, S., Tack, J., Kim, J., & Shin, J. (2024). Optimized Feature Generation for Tabular Data via LLMs with Decision Tree Reasoning. Advances in Neural Information Processing Systems, 38.
• Research Objective: This paper introduces OCTree, a framework that uses LLMs and decision tree reasoning to automate the generation of new features for tabular data, aiming to improve the performance of various prediction models in both classification and regression tasks.
• Methodology: OCTree uses an LLM (specifically, Llama 2 fine-tuned on a dialogue dataset) to generate new column features and their corresponding generation rules. The process starts with the LLM proposing a name for a new column based on the task description. Then, it iteratively refines the rule for generating the values for this new column. The refinement process uses feedback in the form of validation performance scores and decision tree reasoning (extracted from a decision tree trained on the data with the new feature) from previous iterations. This feedback loop continues for a fixed number of iterations, and the rule with the best validation score is selected.
• Key Findings: The authors demonstrate that OCTree consistently improves the performance of various prediction models, including XGBoost, MLP, and HyperFast, on a diverse set of tabular datasets. They show improvements in both context-aware settings (where language descriptions of the features are available) and context-agnostic settings (where such descriptions are absent).
• Main Conclusions: OCTree offers a promising approach to automated feature engineering for tabular data. The use of LLMs allows for the generation of more complex and semantically meaningful features, while decision tree reasoning provides valuable feedback for optimizing the generation rules. The authors suggest that this approach can be scaled to larger, more complex models by transferring features generated using simpler models.
• Significance: This research contributes to the growing field of automated machine learning and highlights the potential of LLMs in addressing key challenges in tabular data analysis. The proposed framework has practical implications for various domains, including healthcare, finance, and academia, where effective feature engineering is crucial for accurate prediction.
• Limitations and Future Research: One limitation is the computational cost associated with evaluating the generated features, especially for complex prediction models. Future research could explore more efficient optimization strategies or leverage techniques like reinforcement learning from human feedback to further enhance the rule generation process.

Статистика

Using OCTree with Llama 2 for XGBoost on the Tesla Stock dataset reduced the relative error by 15.9%.
With GPT-4o, OCTree achieved a relative error reduction of 17.1% on the Tesla Stock dataset for XGBoost.
OCTree outperforms CAAFE with GPT-4o, even when using a custom Llama 2 model fine-tuned on open dialogue data.
On datasets without language descriptions, OCTree reduces relative prediction errors by an average of 5.0% compared to the baseline XGBoost model on 19 classification tasks.
Combining OCTree with OpenFE further boosts performance, achieving a 7.9% reduction in relative error for XGBoost.
Features generated using XGBoost with OCTree can be transferred to improve the performance of MLP and HyperFast models.

Цитаты

Ключевые выводы из

Optimized Feature Generation for Tabular Data via LLMs with Decision Tree Reasoning

by Jaehyun Nam,... в arxiv.org 11-19-2024

https://arxiv.org/pdf/2406.08527.pdf

Дополнительные вопросы

How might the OCTree framework be adapted to handle high-dimensional tabular data with thousands of features?

Scaling OCTree to handle high-dimensional tabular data with thousands of features presents several challenges:

Computational Cost: Evaluating numerous candidate rules by training a prediction model for each iteration becomes computationally expensive with thousands of features.
LLM Context Window: LLMs have limited context windows, making it difficult to process and reason about a vast number of features effectively.
Decision Tree Complexity: Decision trees can become very deep and complex with high-dimensional data, making their interpretation and translation into natural language for LLM feedback challenging.

Here's how OCTree can be adapted to address these challenges:

Feature Subset Selection: Instead of considering all features simultaneously, employ feature selection techniques to identify a smaller subset of potentially relevant features. This could involve:

LLM-based Ranking: Prompt the LLM to rank features based on their perceived importance for the target variable.
Statistical Measures: Utilize feature importance scores from simpler models like XGBoost or statistical tests like ANOVA.
Unsupervised Techniques: Apply dimensionality reduction methods like PCA or feature agglomeration to group similar features.

Hierarchical Feature Representation: Organize features into a hierarchy or clusters based on domain knowledge or data-driven approaches. This allows the LLM to reason about groups of features instead of individual ones, simplifying the optimization process.
Modular Decision Trees: Instead of constructing a single, complex decision tree, use an ensemble of smaller decision trees, each focusing on a specific subset of features. This simplifies interpretation and feedback generation.
Efficient Validation: Explore alternative validation strategies to reduce computational cost:

Proxy Models: Train smaller, faster proxy models to estimate the performance of candidate rules instead of the full prediction model.
Active Learning: Selectively evaluate a subset of promising rules based on their potential for improvement.

LLM Context Extension: Utilize techniques like memory-augmented LLMs or external knowledge bases to extend the effective context window and enable reasoning over larger feature sets.
By implementing these adaptations, OCTree can be scaled to handle high-dimensional tabular data more effectively.

Could the reliance on validation scores for rule optimization be susceptible to overfitting, and how might this be mitigated?

Yes, relying solely on validation scores for rule optimization in OCTree can lead to overfitting, especially with limited data or a large number of optimization iterations. The LLM might learn to exploit specific patterns in the validation set that don't generalize well to unseen data.
Here are some mitigation strategies:

Cross-Validation: Instead of a single validation set, employ k-fold cross-validation to obtain more robust performance estimates and reduce the variance in the optimization process.
Regularization: Introduce regularization techniques to penalize overly complex rules. This could involve:

Limiting Rule Length: Constrain the number of operations or conditions allowed in a rule.
Syntactic Constraints: Guide the LLM to generate simpler rules by imposing grammatical restrictions on the generated code.

Early Stopping: Monitor the performance on a held-out test set during optimization and stop the process if the test performance plateaus or starts to degrade, even if the validation score continues to improve.
Ensemble Methods: Instead of selecting a single best rule, create an ensemble of features generated from different optimization runs or using different random seeds. This can improve generalization by combining diverse perspectives.
Adversarial Validation: Train a separate model to distinguish between the training and validation sets. If the model performs well, it indicates potential data leakage and overfitting to the validation set.
By incorporating these strategies, OCTree can be made more robust to overfitting and produce features that generalize better to unseen data.

What are the ethical implications of using LLMs for automated feature engineering, particularly in sensitive domains like healthcare, where biased data could lead to unfair or inaccurate predictions?

Using LLMs for automated feature engineering in sensitive domains like healthcare raises significant ethical concerns, particularly regarding bias and fairness:

Amplifying Existing Biases: LLMs trained on real-world data can inherit and amplify existing biases present in the data. For example, if historical healthcare data contains biases against certain demographic groups, the LLM might generate features that perpetuate these biases, leading to unfair or inaccurate predictions for those groups.
Creating New Biases: Even without explicitly biased training data, LLMs can develop spurious correlations and generate features that inadvertently discriminate against certain groups. This is particularly concerning when dealing with sensitive attributes like race, gender, or socioeconomic status.
Lack of Transparency: The decision-making process of LLMs can be opaque, making it difficult to understand why certain features are generated and how they might contribute to biased outcomes. This lack of transparency hinders accountability and makes it challenging to identify and mitigate potential biases.
Over-Reliance and Automation Bias: Over-reliance on automated feature engineering without human oversight can lead to automation bias, where decisions made by the system are blindly trusted without critical evaluation, potentially perpetuating harmful biases.
To address these ethical implications, it's crucial to:

Ensure Data Quality and Fairness: Critically examine and pre-process training data to identify and mitigate existing biases. Employ techniques like data augmentation, re-sampling, or adversarial training to promote fairness.
Promote Transparency and Interpretability: Develop methods to interpret and explain the feature generation process of LLMs. This allows for identifying potential biases and understanding the reasoning behind feature selection.
Incorporate Human Oversight and Domain Expertise: Integrate human experts in the loop to review and validate the generated features, ensuring they are ethically sound and align with domain knowledge.
Develop Fairness-Aware Metrics and Constraints: Go beyond accuracy and incorporate fairness-aware metrics to evaluate the performance of generated features and prevent disparate impact on different demographic groups.
Establish Ethical Guidelines and Regulations: Develop clear ethical guidelines and regulations for using LLMs in sensitive domains, ensuring responsible development and deployment of these technologies.
By proactively addressing these ethical considerations, we can harness the potential of LLMs for automated feature engineering while mitigating the risks of perpetuating or amplifying harmful biases in sensitive domains like healthcare.