XGBoost Regressor

Algorithm overview

XGBoostRegressor implements exact-greedy gradient boosting (Chen & Guestrin, 2016) with a regularized objective, growing each tree on first- and second-order gradients of the loss.

This algorithm is especially useful when:

• You want a high-accuracy boosting regressor with explicit regularization.
• You need behavior close to the xgboost library inside a JavaScript runtime.
• Structured tabular data benefits from second-order (Newton) tree growth.

JavaScript implementation

@kanaries/ml provides an exact-greedy XGBoost regressor in JavaScript with the reg:squarederror objective (g = F - y, h = 1). Each tree is grown with the regularized split gain

1/2 * (G_L^2/(H_L+lambda) + G_R^2/(H_R+lambda) - G^2/(H+lambda)) - gamma

and leaf weights -G/(H+lambda), with minChildWeight enforced on the hessian sum. The defaults match the xgboost library (eta=0.3, maxDepth=6, lambda=1, gamma=0, minChildWeight=1, baseScore=0.5), plus subsample and colsampleByTree sampling and a seedable randomState.

Missing values are not supported: there is no sparsity-aware default direction, so NaN/non-finite inputs are rejected with an explicit error rather than silently misrouted.

Quick start

from xgboost import XGBRegressor

X = [[0], [1], [2], [3], [4]]
y = [1.0, 1.8, 3.1, 3.9, 5.2]

reg = XGBRegressor(n_estimators=100, learning_rate=0.3, max_depth=6, reg_lambda=1, random_state=0)
reg.fit(X, y)
pred = reg.predict([[1.5], [3.5]])

import { Ensemble } from '@kanaries/ml';

const X = [[0], [1], [2], [3], [4]];
const y = [1.0, 1.8, 3.1, 3.9, 5.2];

const reg = new Ensemble.XGBoostRegressor({ nEstimators: 100, learningRate: 0.3, maxDepth: 6, lambda: 1, randomState: 0 });
reg.fit(X, y);
const pred = reg.predict([[1.5], [3.5]]);

Quick JavaScript example

import { Ensemble } from '@kanaries/ml';

const X = [[0], [1], [2], [3], [4]];
const y = [1.0, 1.8, 3.1, 3.9, 5.2];

const reg = new Ensemble.XGBoostRegressor({ nEstimators: 100, learningRate: 0.3, maxDepth: 6, lambda: 1, randomState: 0 });
reg.fit(X, y);
const pred = reg.predict([[1.5], [3.5]]);

Detailed API reference

interface XGBoostProps {
    nEstimators?: number;
    learningRate?: number;
    maxDepth?: number;
    lambda?: number;
    gamma?: number;
    minChildWeight?: number;
    subsample?: number;
    colsampleByTree?: number;
    baseScore?: number;
    randomState?: number;
}

constructor(props: XGBoostProps = {})

Every parameter also accepts its snake_case / xgboost alias (n_estimators, learning_rate also as eta, max_depth, reg_lambda, min_child_weight, colsample_bytree, base_score, random_state).

Parameters

Algorithm

The objective is reg:squarederror. Starting from baseScore, each round computes gradients g = F - y and hessians h = 1, then grows an exact-greedy tree that maximizes the regularized split gain and assigns leaf weights -G/(H+lambda). The tree's predictions are added with the learning rate F += learningRate * tree(x). Zero-denominator leaf weights fall back to 0.

Methods

• fit(trainX: number[][], trainY: number[]): void
• predict(testX: number[][]): number[]

Implementation workflow

1. Scale-free tabular features work well; verify inputs are finite (NaN is rejected).
2. Fit with the defaults, then tune maxDepth, learningRate, and nEstimators.
3. Add regularization via lambda, gamma, minChildWeight, subsample, and colsampleByTree if the model overfits.

JavaScript deployment notes

• learningRate (eta) must be in (0, 1]; smaller values usually need more estimators.
• There is no missing-value handling, so impute or drop non-finite inputs before fitting.
• Behavior tracks the xgboost library defaults, making this a drop-in boosting regressor for JS/TS services.