import type { FieldGetterFunction } from '@visactor/vgrammar-util';
export declare function fieldNames(fields: string[] | FieldGetterFunction[], as?: string[]): string[];
export declare function partition(data?: any[], groupBy?: FieldGetterFunction[], field?: FieldGetterFunction): any[];
export declare function sum(arr: any[]): any;
export declare function average(arr: any[]): number;