/**
 * 平均值
 * @param {Array} a
 * @param {Function | String} f
 * @returns
 *
 * Example
 * ```
 * const lowestFirst = myArr.archiveBy("id");
 * ```
 */
export {};
declare global {
    interface Array<T> {
        balance<T>(this: T[]): number;
    }
}