XGBOrdinal

This GitHub repository contains the code used in the paper:

XGBOrdinal: An XGBoost Extension for Ordinal Data
Fabian Kahl, Iris Kahl, Stephan M. Jonas
Presented at MIE 2025
Published in Studies in Health Technology and Informatics, Volume 327, Pages 462–466

Citation

@incollection{kahl2025xgbordinal,
  title={XGBOrdinal: An XGBoost Extension for Ordinal Data},
  author={Kahl, Fabian and Kahl, Iris and Jonas, Stephan M},
  booktitle={Intelligent Health Systems--From Technology to Data and Knowledge},
  pages={462--466},
  year={2025},
  publisher={IOS Press}
}

Installation

You can install XGBOrdinal using pip:

pip install xgbordinal

Alternatively, to install from source:

git clone https://github.com/digital-medicine/XGBOrdinal.git
cd XGBOrdinal
pip install -r requirements.txt

Demos

• ./demo.ipynb to run XGBOrdinal with and without GridSearchCV in Jupyter Notebook.
• ./demo.py to run XGBOrdinal with and without GridSearchCV in Python.

Parameters

XGBOrdinal(aggregation='weighted', norm=True, **extra_params)

• aggregation: str
  • Description: Defines the method for aggregating model across the classifiers.
  • Purpose: Controls how to combine the classifiers. Supported values:
    • 'weighted': Uses class distribution-based weights.
    • 'equal': Uses equal weights for all classifiers.
  • Default: 'weighted'.
• norm: bool
  • Description: Whether to replace all negative outcomes with zero and normalize them so they sum to 1.
  • Purpose: Ensures the outputs are probabilities for each sample.
  • Default: True.
• **extra_params:
  • Description: Additional parameters passed to the underlying XGBClassifiers.
  • Purpose: Customize the underlying classifiers in terms of hyperparameters.
  • Example: 'learning_rate'=0.1, 'max_depth'=3.

Methods

• fit(X, y, **fit_params)
  • Description: Trains multiple binary classifiers based on the ordinal thresholds derived from unique_classes.
  • Parameters:
    • X: The feature matrix for training.
    • y: The target vector for training.
    • **fit_params: Additional parameters passed to the underlying XGBClassifiers (e.g., eval_set).
• predict(X)
  • Description: Predicts the class label for each sample based on the highest predicted probability.
  • Parameters:
    • X: The feature matrix for prediction.
  • Returns: The predicted class labels.
• predict_proba(X)
  • Description: Predicts the probabilities for each ordinal class.
  • Parameters:
    • X: The feature matrix for prediction.
  • Returns: A 2D array where each row contains the predicted probabilities for each class.
  • Note: If norm=True, the probabilities will sum to 1 for each sample.
• feature_importance(importance_type='gain')
  • Description: Computes feature importance across all classifiers, aggregated using the specified aggregation strategy.
  • Parameters:
    • importance_type: Type of XGBoost importance to compute (e.g., 'gain', 'weight', 'cover').
  • Returns: A dictionary of feature importance scores.

Folder Structure

• ./experiments contains the experiments of the paper.