lodash/collection/indexBy.js

define(['../internal/createAggregator'], function(createAggregator) {

  /**
   * Creates an object composed of keys generated from the results of running
   * each element of `collection` through `iteratee`. The corresponding value
   * of each key is the last element responsible for generating the key. The
   * iteratee function is bound to `thisArg` and invoked with three arguments;
   * (value, index|key, collection).
   *
   * If a property name is provided for `predicate` the created `_.property`
   * style callback returns the property value of the given element.
   *
   * If a value is also provided for `thisArg` the created `_.matchesProperty`
   * style callback returns `true` for elements that have a matching property
   * value, else `false`.
   *
   * If an object is provided for `predicate` the created `_.matches` style
   * callback returns `true` for elements that have the properties of the given
   * object, else `false`.
   *
   * @static
   * @memberOf _
   * @category Collection
   * @param {Array|Object|string} collection The collection to iterate over.
   * @param {Function|Object|string} [iteratee=_.identity] The function invoked
   *  per iteration.
   * @param {*} [thisArg] The `this` binding of `iteratee`.
   * @returns {Object} Returns the composed aggregate object.
   * @example
   *
   * var keyData = [
   *   { 'dir': 'left', 'code': 97 },
   *   { 'dir': 'right', 'code': 100 }
   * ];
   *
   * _.indexBy(keyData, 'dir');
   * // => { 'left': { 'dir': 'left', 'code': 97 }, 'right': { 'dir': 'right', 'code': 100 } }
   *
   * _.indexBy(keyData, function(object) { return String.fromCharCode(object.code); });
   * // => { 'a': { 'dir': 'left', 'code': 97 }, 'd': { 'dir': 'right', 'code': 100 } }
   *
   * _.indexBy(keyData, function(object) { return this.fromCharCode(object.code); }, String);
   * // => { 'a': { 'dir': 'left', 'code': 97 }, 'd': { 'dir': 'right', 'code': 100 } }
   */
  var indexBy = createAggregator(function(result, value, key) {
    result[key] = value;
  });

  return indexBy;
});