import { Selector, Predicate } from '../types';
/**
 * Sum of items in array.
 * @param array The array to process.
 * @param elementSelector Function invoked per iteration.
 * @returns Sum of array.
 * @public
 * @example
 * sum([1, 2, 5]); // 8
 *
 * sum([{ val: 1 }, { val: 5 }], i => i.val); // 6
 */
export declare function sum(array: any[], field?: Selector | string): number | null;
/**
 * Average of array items.
 * @param array The array to process.
 * @param elementSelector Function invoked per iteration.
 * @public
 * @example
 * avg([1, 5, 3]); // 3
 */
export declare function avg(array: any[], field?: Selector | string): number | null;
/**
 * Computes the minimum value of array.
 * @param array The array to process.
 * @param elementSelector Function invoked per iteration.
 */
export declare function min(array: any[], field?: Selector | string): number | Date | null;
/**
 * Computes the maximum value of array.
 * @public
 * @param array The array to process.
 * @param elementSelector Function invoked per iteration.
 */
export declare function max(array: any[], field?: Selector | string): number | Date | null;
/**
 * Count of elements in array.
 * @public
 * @param array The array to process.
 * @param predicate Predicate function invoked per iteration.
 */
export declare function count(array: any[], predicate?: Predicate): number | null;
/**
 * Gets first item in array satisfies predicate.
 * @param array The array to process.
 * @param predicate Predicate function invoked per iteration.
 */
export declare function first<T = any>(array: T[], predicate?: Predicate): T | null;
/**
 * Gets last item in array satisfies predicate.
 * @param array The array to process.
 * @param predicate Predicate function invoked per iteration.
 */
export declare function last<T = any>(array: T[], predicate?: Predicate): T | null;
/**
 * Gets counts map of values returned by `elementSelector`.
 * @param array The array to process.
 * @param elementSelector Function invoked per iteration.
 */
export declare function countBy(array: any[], elementSelector: Selector): Record<string, number>;
/**
 * Get mean of an array.
 * @param array The array to process.
 * @param field Property name or Selector function invoked per iteration.
 */
export declare function mean(array: any[], field?: Selector | string): number | null;
/**
 * Get quantile of a sorted array.
 * @param array The array to process.
 * @param field Property name or Selector function invoked per iteration.
 * @param p quantile.
 */
export declare function quantile(array: any[], p: number, field?: Selector | string): number | null;
/**
 * Get sample variance of an array.
 * @param array The array to process.
 * @param field Property name or Selector function invoked per iteration.
 */
export declare function variance(array: any[], field?: Selector | string): number | null;
/**
 * Get the sample standard deviation of an array.
 * @param array The array to process.
 * @param field Property name or Selector function invoked per iteration.
 */
export declare function stdev(array: any[], field?: Selector | string): number | null;
/**
 * Get median of an array.
 * @param array The array to process.
 * @param field Property name or Selector function invoked per iteration.
 */
export declare function median(array: any[], field?: Selector | string): number | null;
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