ctboost 0.1.5

A GPU-accelerated gradient boosting library using Conditional Inference Trees.

CTBoost

CTBoost is a gradient boosting library built around Conditional Inference Trees, with a native C++17 core, Python bindings via pybind11, optional CUDA support for source builds, and a scikit-learn style API.

The current codebase supports end-to-end training and prediction for regression, classification, and grouped ranking, plus pandas and SciPy sparse ingestion, row weights and class imbalance controls, explicit missing-value handling, configurable validation metrics, stable JSON model persistence, staged prediction, warm-start continuation, and a built-in cross-validation helper.

Current Status

• Language mix: Python + C++17, with optional CUDA
• Python support: 3.8 through 3.14
• Packaging: scikit-build-core
• CI/CD: GitHub Actions for CMake validation and cibuildwheel release builds
• Status: actively evolving native + Python package

What Works Today

• Native gradient boosting backend exposed as ctboost._core
• Pool abstraction for dense tabular data, SciPy sparse input, categorical feature indices, and optional group_id
• Native pandas DataFrame and Series support
• Automatic categorical detection for pandas category and object columns
• Regression training with ctboost.train(...)
• scikit-learn compatible CTBoostClassifier, CTBoostRegressor, and CTBoostRanker
• Binary and multiclass classification
• Grouped ranking with PairLogit and NDCG
• Row weights through Pool(..., weight=...) and sample_weight on sklearn estimators
• Class imbalance controls through class_weight, class_weights, auto_class_weights="balanced", and scale_pos_weight
• Explicit missing-value handling through nan_mode
• Early stopping with eval_set and early_stopping_rounds
• Separate eval_metric support for validation history and early stopping
• Validation loss/metric history and evals_result_
• Per-iteration prediction through staged prediction and num_iteration
• Stable JSON and pickle model persistence for low-level boosters and scikit-learn style estimators
• Cross-validation with ctboost.cv(...)
• Regression objectives: RMSE, MAE, Huber, Quantile
• Generic eval metrics including RMSE, MAE, Accuracy, Precision, Recall, F1, AUC, and NDCG
• Feature importance reporting
• Leaf-index introspection and path-based prediction contributions
• Continued training through init_model and estimator warm_start
• Build metadata reporting through ctboost.build_info()
• CPU builds on standard CI runners
• Optional CUDA compilation when building from source with a suitable toolkit

Current Limitations

• SciPy sparse matrices are currently densified at the Python boundary before native training
• Dedicated GPU wheel automation targets Linux x86_64 CPython 3.10 through 3.14 release assets for Kaggle-style environments
• CUDA wheel builds in CI depend on container-side toolkit provisioning

Installation

For local development or source builds:

pip install .

Install development dependencies:

pip install -e .[dev]

Wheels vs Source Builds

pip install ctboost works without a compiler only when PyPI has a prebuilt wheel for your exact Python/OS tag. If no matching wheel exists, pip falls back to the source distribution and has to compile the native extension locally.

The release workflow is configured to publish CPU wheels for current CPython releases on Windows, Linux, and macOS so standard pip install ctboost usage does not depend on a local compiler.

Each tagged GitHub release also attaches the CPU wheels, the source distribution, and dedicated Linux x86_64 CUDA wheels for CPython 3.10 through 3.14. The GPU wheel filenames carry a 1gpu build tag so the release can publish CPU and GPU artifacts for the same Python and platform tags without filename collisions.

The tag release workflow skips the in-container GPU wheel smoke test for these Linux CUDA assets. GitHub's manylinux build containers do not provide a Kaggle-like NVIDIA runtime, so the GPU wheels are published as release assets for downstream validation on real CUDA hosts such as Kaggle.

Kaggle GPU Install

pip install ctboost still resolves to the CPU wheel on PyPI. On Kaggle, install the matching GPU release wheel from GitHub instead:

import json
import subprocess
import sys
import urllib.request

tag = "v0.1.5"
py_tag = f"cp{sys.version_info.major}{sys.version_info.minor}"
api_url = f"https://api.github.com/repos/captnmarkus/ctboost/releases/tags/{tag}"

with urllib.request.urlopen(api_url) as response:
    release = json.load(response)

asset = next(
    item
    for item in release["assets"]
    if item["name"].endswith(".whl") and f"-1gpu-{py_tag}-{py_tag}-" in item["name"]
)

subprocess.check_call(
    [sys.executable, "-m", "pip", "install", "-U", asset["browser_download_url"]]
)

After installation, confirm the wheel really contains CUDA support:

import ctboost

print(ctboost.build_info())

CPU-Only Source Build

To force a CPU-only native build:

CMAKE_ARGS="-DCTBOOST_ENABLE_CUDA=OFF" pip install .

On PowerShell:

$env:CMAKE_ARGS="-DCTBOOST_ENABLE_CUDA=OFF"
pip install .

Windows source builds require a working C++ toolchain. In practice that means Visual Studio Build Tools 2022 or a compatible MSVC environment, plus CMake. ninja is recommended, but it does not replace the compiler itself.

CUDA Source Build

CTBoost can compile a CUDA backend when the CUDA toolkit and compiler are available. CUDA is enabled by default in CMake, but the build automatically falls back to CPU-only when no toolkit is detected.

pip install .

You can inspect the compiled package after installation:

import ctboost
print(ctboost.build_info())

Quick Start

scikit-learn Style Classification

import pandas as pd
from sklearn.datasets import make_classification

from ctboost import CTBoostClassifier

X, y = make_classification(
    n_samples=256,
    n_features=8,
    n_informative=5,
    n_redundant=0,
    random_state=13,
).astype("float32")
X = pd.DataFrame(X, columns=[f"f{i}" for i in range(X.shape[1])])
X["segment"] = pd.Categorical(["a" if i % 2 == 0 else "b" for i in range(len(X))])
y = y.astype("float32")

model = CTBoostClassifier(
    iterations=256,
    learning_rate=0.1,
    max_depth=3,
    alpha=1.0,
    lambda_l2=1.0,
    task_type="CPU",
)

model.fit(
    X.iloc[:200],
    y[:200],
    eval_set=[(X.iloc[200:], y[200:])],
    early_stopping_rounds=20,
)
proba = model.predict_proba(X)
pred = model.predict(X)
importance = model.feature_importances_
best_iteration = model.best_iteration_

Low-Level Training API

import numpy as np

import ctboost

X = np.array([[0.0, 1.0], [1.0, 0.0], [0.5, 0.5]], dtype=np.float32)
y = np.array([0.0, 1.0, 0.5], dtype=np.float32)

pool = ctboost.Pool(X, y)
booster = ctboost.train(
    pool,
    {
        "objective": "Huber",
        "learning_rate": 0.2,
        "max_depth": 2,
        "alpha": 1.0,
        "lambda_l2": 1.0,
        "max_bins": 64,
        "huber_delta": 1.5,
        "eval_metric": "MAE",
        "nan_mode": "Min",
        "task_type": "CPU",
    },
    num_boost_round=10,
)

predictions = booster.predict(pool)
loss_history = booster.loss_history
eval_loss_history = booster.eval_loss_history

Working With Categorical Features

Categorical columns can still be marked manually through the Pool API:

import numpy as np
import ctboost

X = np.array([[0.0], [1.0], [2.0], [3.0]], dtype=np.float32)
y = np.array([1.0, 0.0, 1.0, 0.0], dtype=np.float32)

pool = ctboost.Pool(X, y, cat_features=[0])

For pandas inputs, categorical/object columns are detected automatically:

import pandas as pd
import ctboost

frame = pd.DataFrame(
    {
        "value": [1.0, 2.0, 3.0, 4.0],
        "city": pd.Categorical(["berlin", "paris", "berlin", "rome"]),
        "segment": ["retail", "enterprise", "retail", "enterprise"],
    }
)
label = pd.Series([0.0, 1.0, 0.0, 1.0], dtype="float32")

pool = ctboost.Pool(frame, label)
assert pool.cat_features == [1, 2]

Model Persistence, Warm Start, And Cross-Validation

import ctboost

booster.save_model("regression-model.json")
restored = ctboost.load_model("regression-model.json")
restored_predictions = restored.predict(pool)

continued = ctboost.train(
    pool,
    {"objective": "RMSE", "learning_rate": 0.2, "max_depth": 2, "alpha": 1.0, "lambda_l2": 1.0},
    num_boost_round=10,
    init_model=restored,
)

cv_result = ctboost.cv(
    pool,
    {
        "objective": "RMSE",
        "learning_rate": 0.2,
        "max_depth": 2,
        "alpha": 1.0,
        "lambda_l2": 1.0,
    },
    num_boost_round=25,
    nfold=3,
)

The scikit-learn compatible estimators also expose:

• save_model(...)
• load_model(...)
• staged_predict(...)
• staged_predict_proba(...) for classifiers
• predict_leaf_index(...)
• predict_contrib(...)
• evals_result_
• best_score_
• sample_weight on fit(...)
• class_weight, scale_pos_weight, eval_metric, nan_mode, and warm_start

Public Python API

The main entry points are:

• ctboost.Pool
• ctboost.train
• ctboost.cv
• ctboost.Booster
• ctboost.CTBoostClassifier
• ctboost.CTBoostRanker
• ctboost.CTBoostRegressor
• ctboost.CBoostClassifier
• ctboost.CBoostRanker
• ctboost.CBoostRegressor
• ctboost.build_info
• ctboost.load_model

Build and Test

Run the test suite:

pytest tests

Build an sdist:

python -m build --sdist

Configure and build the native extension directly with CMake:

python -m pip install pybind11 numpy pandas scikit-learn pytest
cmake -S . -B build -DCTBOOST_ENABLE_CUDA=OFF -Dpybind11_DIR="$(python -m pybind11 --cmakedir)"
cmake --build build --config Release --parallel

Wheel builds are configured through cibuildwheel for:

• Windows amd64
• Linux x86_64 and aarch64 using the current manylinux baseline
• macOS universal2
• CPython 3.8, 3.9, 3.10, 3.11, 3.12, 3.13, and 3.14

GitHub Actions workflows:

• .github/workflows/cmake.yml: configures, builds, installs, and tests CPU builds on Ubuntu, Windows, and macOS for pushes and pull requests
• .github/workflows/publish.yml: builds release wheels and the sdist, runs wheel smoke tests on built artifacts, publishes CPU wheels to PyPI, and attaches both CPU and Linux GPU wheels to tagged GitHub releases

The standard PyPI release wheel workflow builds CPU-only wheels by setting:

cmake.define.CTBOOST_ENABLE_CUDA=OFF

The Linux GPU release-wheel matrix enables CUDA separately with:

cmake.define.CTBOOST_ENABLE_CUDA=ON
wheel.build-tag=1gpu

Project Layout

ctboost/      Python API layer
include/      public C++ headers
src/core/     core boosting, objectives, trees, statistics
src/bindings/ pybind11 extension bindings
cuda/         optional CUDA backend
tests/        Python test suite

License

Apache 2.0. See LICENSE.