/**
 * Abstract class for custom aggregation operations.
 */
export class Reducer {
    constructor(outputs: any);
    _outputs: any;
    size(): any;
    outputs(): any;
    init(columns: any): {};
    add(state: any, row: any, data: any): void;
    rem(state: any, row: any, data: any): void;
    write(state: any, values: any, index: any): void;
}