从数组中计算出每个数的个数

学习到一个新办法

'use strict';

function grouping_count(collection) {

return collection.reduce((p,k) => (p[k]++ || (p[k] = 1),p),{});

}

module.exports = grouping_count;

测试文件

'use strict';var grouping_count = require("../../practices/filter/grouping_count.js");describe('grouping_count', function() {var collection = [1,1,1,1,2,3,1,3,4,2,3,1,3,4,2];iit('从collection中计算出每个数的个数', function() {var result = grouping_count(collection);expect(result).toEqual({'1':6, '2':3, '3':4, '4':2});})});