export declare function std<T = any>(arr: T[], size: number, rng?: () => number): T[];
export interface TrainTestSplitOptions {
    /** Fraction in (0, 1) or absolute count; defaults to 0.25 when trainSize is also unset. */
    testSize?: number;
    /** Fraction in (0, 1) or absolute count; defaults to the complement of testSize. */
    trainSize?: number;
    shuffle?: boolean;
    randomState?: number;
    /** Class labels; when given, the split preserves per-class proportions (requires shuffle). */
    stratify?: any[];
}
export interface TrainTestSplitResult<X = any, Y = any> {
    XTrain: X[];
    XTest: X[];
    yTrain?: Y[];
    yTest?: Y[];
}
/**
 * Split `total` across categories proportionally to `counts` (largest-remainder
 * rounding, deterministic ties by category order); never allocates more than a
 * category's count. Used by stratified train/test splitting.
 */
export declare function allocateProportionally(counts: number[], total: number, random?: () => number): number[];
export declare function trainTestSplit<X = any, Y = any>(X: X[], y?: Y[], options?: TrainTestSplitOptions): TrainTestSplitResult<X, Y>;