average-new.ts

import { identityAsync } from '../util/identity';
import { wrapWithAbort } from './operators/withabort';
import { throwIfAborted } from '../aborterror';

/**
 * The options for calculating an average.
 *
 * @export
 * @interface AverageOptions
 * @template T The type of elements in the source sequence.
 */
export interface AverageOptions<T> {
  /**
   * An optional selector used to get the value to average.
   *
   * @memberof AverageOptions
   */
  selector?: (x: T, signal?: AbortSignal) => number | Promise<number>;
  /**
   * An optional thisArg for the selector.
   *
   * @type {*}
   * @memberof AverageOptions
   */
  thisArg?: any;
  /**
   * An optional abort signal to cancel the operation at any time.
   *
   * @type {AbortSignal}
   * @memberof AverageOptions
   */
  signal?: AbortSignal;
}

/**
 * Computes the average of the async-iterable sequence.
 *
 * @export
 * @param {AsyncIterable<number>} source The source async-iterable sequence to compute the average.
 * @returns {Promise<number>} A Promise which returns the computed average for the async-iterable sequence.
 */
export async function average(
  source: AsyncIterable<number>,
  options?: AverageOptions<number>
): Promise<number>;
/**
 * Computes the average of the async-iterable sequence.
 *
 * @export
 * @template TSource The type of elements in the source sequence.
 * @param {AsyncIterable<TSource>} source source async-iterable sequence to compute the average.
 * @param {((x: TSource, signal?: AbortSignal) => number | Promise<number>)} [selector] An optional selector used to get the value to average.
 * @param {*} [thisArg] An optional thisArg for the selector.
 * @param {AbortSignal} [signal] An optional abort signal to cancel the operation at any time.
 * @returns {Promise<number>} A Promise which returns the computed average for the async-iterable sequence.
 */
export async function average<TSource>(
  source: AsyncIterable<TSource>,
  options?: AverageOptions<TSource>
): Promise<number>;
/**
 * Computes the average of the async-iterable sequence.
 *
 * @export
 * @param {AsyncIterable<any>} source source async-iterable sequence to compute the average.
 * @param {((x: any, signal?: AbortSignal) => number | Promise<number>)} [selector=identityAsync] An optional selector used to get the value
 * to average.
 * @param {*} [thisArg] An optional thisArg for the selector.
 * @param {AbortSignal} [signal] An optional abort signal to cancel the operation at any time.
 * @returns {Promise<number>} A Promise which returns the computed average for the async-iterable sequence.
 */
export async function average(
  source: AsyncIterable<any>,
  options?: AverageOptions<any>
): Promise<number> {
  const opts = options || { };
  if (!opts.selector) {
    opts.selector = identityAsync;
  }
  const { selector, signal, thisArg } = opts;
  throwIfAborted(signal);
  let sum = 0;
  let count = 0;
  for await (const item of wrapWithAbort(source, signal)) {
    sum += await selector!.call(thisArg, item, signal);
    count++;
  }

  if (count === 0) {
    throw new Error('Empty collection');
  }

  return sum / count;
}

average-old.ts

import { identityAsync } from '../util/identity';
import { wrapWithAbort } from './operators/withabort';
import { throwIfAborted } from '../aborterror';

/**
 * Computes the average of the async-iterable sequence.
 * @param source The source async-iterable sequence to compute the average.
 * @param selector The selector used to get the value to average.
 * @param thisArg An optional thisArg for the selector.
 * @param signal An optional abort signal to cancel the operation at any time.
 */
export async function average(
  source: AsyncIterable<number>,
  selector?: (x: number, signal?: AbortSignal) => number | Promise<number>,
  thisArg?: any,
  signal?: AbortSignal
): Promise<number>;
export async function average<TSource>(
  source: AsyncIterable<TSource>,
  selector?: (x: TSource, signal?: AbortSignal) => number | Promise<number>,
  thisArg?: any,
  signal?: AbortSignal
): Promise<number>;
export async function average(
  source: AsyncIterable<any>,
  selector: (x: any, signal?: AbortSignal) => number | Promise<number> = identityAsync,
  thisArg?: any,
  signal?: AbortSignal
): Promise<number> {
  throwIfAborted(signal);
  let sum = 0;
  let count = 0;
  for await (const item of wrapWithAbort(source, signal)) {
    sum += await selector.call(thisArg, item, signal);
    count++;
  }

  if (count === 0) {
    throw new Error('Empty collection');
  }

  return sum / count;
}