javascript - 通过比较获取最大 Underscore.js

Question

有没有办法在underscore.js的帮助下通过比较user_id和assess_id来获得最大时间值，所以user_id和assess_id是一种复合

列表将是

var list = [
      {user_id: 316,asess_id:1,time:1418109860},
      {user_id: 316,asess_id:1,time:1417708379},
      {user_id: 316,asess_id:1,time:1417708231},
      {user_id: 316,asess_id:2,time:1417708379},
      {user_id: 316,asess_id:2,time:1417692420},
      {user_id: 5092,asess_id:2,time:1417692141},
      {user_id: 316,asess_id:1,time:1417633200},
      {user_id: 5092,asess_id:1,time:1417633200},
      {user_id: 448,asess_id:1,time:1417633200}
    ];

必填答案是

var answer = [
      {user_id: 316,asess_id:1,time:1418109860},
      {user_id: 316,asess_id:2,time:1417708379},
      {user_id: 5092,asess_id:2,time:1417692141},
      {user_id: 5092,asess_id:1,time:1417633200},
      {user_id: 448,asess_id:1,time:1417633200}
    ];

虽然我知道一个解决方案，我循环遍历整个列表并开始填写答案，并在答案中输入数据时检查重复值，但我已经实现了这个解决方案。想学习Underscore.js的帮助下是否可以

Answer 1

您可以组合使用 groupBy 和 map/max 方法:

var result = _.chain(list)
    .groupBy(function(el) {
        return el.user_id + ',' + el.asess_id;
    })
    .map(function(obj) {
        return _.max(obj, 'time');
    })
    .value();

查看下面的测试演示。

var list = [
    {user_id: 316,asess_id:1,time:1418109860},
    {user_id: 316,asess_id:1,time:1417708379},
    {user_id: 316,asess_id:1,time:1417708231},
    {user_id: 316,asess_id:2,time:1417708379},
    {user_id: 316,asess_id:2,time:1417692420},
    {user_id: 5092,asess_id:2,time:1417692141},
    {user_id: 316,asess_id:1,time:1417633200},
    {user_id: 5092,asess_id:1,time:1417633200},
    {user_id: 448,asess_id:1,time:1417633200}
];

var result = _.chain(list)
    .groupBy(function(el) {
        return el.user_id + ',' + el.asess_id;
    })
    .map(function(obj) {
        return _.max(obj, 'time')
    })
    .value();

alert(JSON.stringify(result, null, 4));

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