countBy.js (1262B)
1 var baseAssignValue = require('./_baseAssignValue'), 2 createAggregator = require('./_createAggregator'); 3 4 /** Used for built-in method references. */ 5 var objectProto = Object.prototype; 6 7 /** Used to check objects for own properties. */ 8 var hasOwnProperty = objectProto.hasOwnProperty; 9 10 /** 11 * Creates an object composed of keys generated from the results of running 12 * each element of `collection` thru `iteratee`. The corresponding value of 13 * each key is the number of times the key was returned by `iteratee`. The 14 * iteratee is invoked with one argument: (value). 15 * 16 * @static 17 * @memberOf _ 18 * @since 0.5.0 19 * @category Collection 20 * @param {Array|Object} collection The collection to iterate over. 21 * @param {Function} [iteratee=_.identity] The iteratee to transform keys. 22 * @returns {Object} Returns the composed aggregate object. 23 * @example 24 * 25 * _.countBy([6.1, 4.2, 6.3], Math.floor); 26 * // => { '4': 1, '6': 2 } 27 * 28 * // The `_.property` iteratee shorthand. 29 * _.countBy(['one', 'two', 'three'], 'length'); 30 * // => { '3': 2, '5': 1 } 31 */ 32 var countBy = createAggregator(function(result, value, key) { 33 if (hasOwnProperty.call(result, key)) { 34 ++result[key]; 35 } else { 36 baseAssignValue(result, key, 1); 37 } 38 }); 39 40 module.exports = countBy;