oqboost 2.1.1

OQBoost 2.0 — gradient-boosted 2D-oblique decision trees (histogram-binned, C++ backend)

OQBoost 2.0

Gradient-boosted 2D-oblique decision trees — histogram-binned, C++ backend.

OQBoost splits on oblique hyperplanes over feature pairs (a·u + b·v < t) instead of axis-aligned thresholds, so diagonal and interaction boundaries are represented directly rather than as axis-aligned approximations. Version 2.0 is a histogram-binned 2D-oblique core that finds split directions by H-weighted least-squares regression of the gradient — deterministic, one 2×2 solve per feature pair (no random projections or numerical search).

scikit-learn compatible · compiled C++ (pybind11) + OpenMP · native missing-value handling (NaN routed to a learned bin, no imputation needed).

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Install

pip install oqboost

Prebuilt wheels are provided for Windows, macOS (arm64), and Ubuntu/Linux via cibuildwheel. On other platforms pip builds from source — needs a C++17 compiler (clang++/g++) and, for parallelism, OpenMP (brew install libomp on macOS).

Quickstart

from oqboost import OQBoostClassifier, OQBoostRegressor

# Binary classification
clf = OQBoostClassifier(
    n_estimators=120, learning_rate=0.06, max_depth=4,
    max_bins=16, subsample=0.8, colsample=0.8, random_state=42,
)
clf.fit(X_train, y_train)
proba = clf.predict_proba(X_test)[:, 1]   # P(class 1)
pred  = clf.predict(X_test)

# Multiclass — pass a target with 3+ classes; handled one-vs-rest automatically
clf.fit(X_train, y_multiclass)
proba = clf.predict_proba(X_test)         # (n_samples, n_classes), rows sum to 1
labels = clf.predict(X_test)

# Regression (squared error)
reg = OQBoostRegressor(n_estimators=120, learning_rate=0.06)
reg.fit(X_train, y_train)
y_hat = reg.predict(X_test)

Both are drop-in scikit-learn estimators — usable in Pipeline, GridSearchCV, cross_val_score, and clone.

More features

# Imbalanced data: tune the decision threshold on a holdout (probabilities stay
# calibrated; "balanced" maximizes balanced accuracy, "f1" maximizes F1).
clf = OQBoostClassifier(threshold="balanced").fit(X_train, y_train)
clf.decision_threshold_          # the chosen cut

# Robust regression: huber / quantile losses (init = median), optional output clip.
reg = OQBoostRegressor(loss="huber", alpha=0.9, clip=True).fit(X_train, y_train)
q90 = OQBoostRegressor(loss="quantile", alpha=0.9).fit(X_train, y_train)  # 90th pctile

# Monotonic constraints (-1 / 0 / +1 per feature; list or {index: dir} dict),
# enforced through the oblique splits.
reg = OQBoostRegressor(monotone_constraints={0: +1, 3: -1}).fit(X_train, y_train)

# Incremental training: add trees without refitting from scratch.
clf = OQBoostClassifier(n_estimators=100, warm_start=True).fit(X_train, y_train)
clf.set_params(n_estimators=200).fit(X_train, y_train)   # trains only +100 trees

# Serialization: models are pickle / joblib compatible out of the box.
import pickle, joblib
pickle.dump(clf, open("clf.pkl", "wb"))
clf2 = pickle.load(open("clf.pkl", "rb"))
joblib.dump(clf, "clf.joblib")

# Native explanations (no SHAP dependency)
clf.feature_importances_         # Σ gain per feature
clf.coefficient_importances_     # Σ gain·|coef| (direction-weighted)
clf.interaction_importances_     # d×d matrix, Σ gain·|a|·|b| — learned feature pairs
phi = clf.explain(X_test)        # additive contributions — (n, n_features) for binary/
                                 # regression, (n, n_classes, n_features) for multiclass
                                 # phi.sum(axis=-1) == raw score − base (like SHAP)

# Plots (pip install oqboost[plot])
import oqboost.plot as oqp
oqp.plot_importance(clf)              # gain / gain·|coef| bar
oqp.plot_interactions(clf)           # pairwise-interaction heatmap
oqp.plot_explanation(clf, x)         # one-sample additive contributions
oqp.plot_explanation_summary(clf, X) # SHAP-style beeswarm

Key hyperparameters

Param	Default	Meaning
n_estimators	120	boosting rounds
learning_rate	0.06	shrinkage
max_depth	4	interaction depth (stacked 2D cuts)
max_bins	16	grid / direction-seed resolution (keep small)
subsample	0.8	rows per tree (key overfit lever)
colsample	0.8	features per node
reg_lambda	1.0	L2 regularization
n_screen	-1	SIS top-m feature screening (-1 = exhaustive)
threshold	"0.5"	binary decision cut — "balanced"/"f1" tunes it on a holdout (imbalanced data)
loss	"squared"	regression loss — "huber"/"quantile" are outlier-robust
alpha	0.9	huber δ-quantile / quantile target
clip	False	clamp regression output to training target range
monotone_constraints	None	per-feature monotonicity -1/0/+1 (list or {idx: dir} dict)
warm_start	False	add trees on top of the existing model when n_estimators grows (incremental)
categorical_features	None	indices / bool mask of categorical columns → lossless binning (no level merging)
max_lineage	0	LOB (experimental): >0 approximates high-order oblique interactions with only 2×2 solves — nodes inherit ancestor directions ((z,x)/(z,z) pairs) and compose them across depth. 0 = classic 2D

Why oblique

Axis-aligned boosters need several stacked cuts to approximate a diagonal boundary, while an oblique split represents it directly. On 2D problems (XOR, Spiral, Checkerboard) OQBoost draws the diagonal boundary with oblique cuts rather than axis-aligned steps. On Optuna-tuned tabular benchmarks it is competitive with the established gradient-boosting libraries.

Full benchmarks, decision-boundary figures, and design notes: https://github.com/cree1116/oqboost-2.0

Note: OQBoost 2.0 is a ground-up rewrite. The original 1.x line — oblique splits via a Deterministic Gradient-Covariance Scan (DGCS) — lives at cree1116/OQBoost. 2.0 replaces the direction finder with a histogram-binned H-weighted gradient-regression fit (one 2×2 solve per pair).

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MIT License.