partition.js

var createAggregator = require('../internal/createAggregator');

/**
 * Creates an array of elements split into two groups, the first of which
 * contains elements `predicate` returns truthy for, while the second of which
 * contains elements `predicate` returns falsey for. The predicate 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} [predicate=_.identity] The function invoked
 *  per iteration.
 * @param {*} [thisArg] The `this` binding of `predicate`.
 * @returns {Array} Returns the array of grouped elements.
 * @example
 *
 * _.partition([1, 2, 3], function(n) {
 *   return n % 2;
 * });
 * // => [[1, 3], [2]]
 *
 * _.partition([1.2, 2.3, 3.4], function(n) {
 *   return this.floor(n) % 2;
 * }, Math);
 * // => [[1.2, 3.4], [2.3]]
 *
 * var users = [
 *   { 'user': 'barney',  'age': 36, 'active': false },
 *   { 'user': 'fred',    'age': 40, 'active': true },
 *   { 'user': 'pebbles', 'age': 1,  'active': false }
 * ];
 *
 * var mapper = function(array) {
 *   return _.pluck(array, 'user');
 * };
 *
 * // using the `_.matches` callback shorthand
 * _.map(_.partition(users, { 'age': 1, 'active': false }), mapper);
 * // => [['pebbles'], ['barney', 'fred']]
 *
 * // using the `_.matchesProperty` callback shorthand
 * _.map(_.partition(users, 'active', false), mapper);
 * // => [['barney', 'pebbles'], ['fred']]
 *
 * // using the `_.property` callback shorthand
 * _.map(_.partition(users, 'active'), mapper);
 * // => [['fred'], ['barney', 'pebbles']]
 */
var partition = createAggregator(function(result, value, key) {
  result[key ? 0 : 1].push(value);
}, function() { return [[], []]; });

module.exports = partition;