Underscore.JS - countBy 方法

语法

_.countBy(list, iteratee, [context])

countBy 方法根据提供的迭代函数返回的值获取已分裂列表的计数。

示例

var _ = require('underscore');

var list = [{"title": "Learn Java", "Author": "Sam", "Cost": 200},
   {"title": "Learn Scala", "Author": "Sam", "Cost": 200},
   {"title": "Learn C", "Author": "Julie", "Cost": 200} ]

//Example 1. invoke countBy method to get book count written by Authors
var result = _.countBy(list, 'Author');
console.log(result);

//Example 2. invoke countBy method to get book count by their cost
result = _.countBy(list, 'Cost')
console.log(result)

在 tester.js 中保存上述程序。运行以下命令以执行此程序。

命令

\>node tester.js

输出

{ Sam: 2, Julie: 1 }
{ '200': 3 }