import { AccumulatorOperator } from "../../types";
/**
 * Returns an average of all the values in a group.
 *
 * @param {Array} collection The input array
 * @param {AnyObject} expr The right-hand side expression value of the operator
 * @param {Options} options The options to use for this operation
 * @returns {Number}
 */
export declare const $avg: AccumulatorOperator;