Async.js

groupBy.js

  1. import doLimit from './internal/doLimit';
  2. import groupByLimit from './groupByLimit';
  4. /**
  5.  * Returns a new object, where each value corresponds to an array of items, from
  6.  * `coll`, that returned the corresponding key. That is, the keys of the object
  7.  * correspond to the values passed to the `iteratee` callback.
  8.  *
  9.  * Note: Since this function applies the `iteratee` to each item in parallel,
  10.  * there is no guarantee that the `iteratee` functions will complete in order.
  11.  * However, the values for each key in the `result` will be in the same order as
  12.  * the original `coll`. For Objects, the values will roughly be in the order of
  13.  * the original Objects' keys (but this can vary across JavaScript engines).
  14.  *
  15.  * @name groupBy
  16.  * @static
  17.  * @memberOf module:Collections
  18.  * @method
  19.  * @category Collection
  20.  * @param {Array|Iterable|Object} coll - A collection to iterate over.
  21.  * @param {AsyncFunction} iteratee - An async function to apply to each item in
  22.  * `coll`.
  23.  * The iteratee should complete with a `key` to group the value under.
  24.  * Invoked with (value, callback).
  25.  * @param {Function} [callback] - A callback which is called when all `iteratee`
  26.  * functions have finished, or an error occurs. Result is an `Object` whoses
  27.  * properties are arrays of values which returned the corresponding key.
  28.  * @example
  29.  *
  30.  * async.groupBy(['userId1', 'userId2', 'userId3'], function(userId, callback) {
  31.  *     db.findById(userId, function(err, user) {
  32.  *         if (err) return callback(err);
  33.  *         return callback(null, user.age);
  34.  *     });
  35.  * }, function(err, result) {
  36.  *     // result is object containing the userIds grouped by age
  37.  *     // e.g. { 30: ['userId1', 'userId3'], 42: ['userId2']};
  38.  * });
  39.  */
  40. export default doLimit(groupByLimit, Infinity);