如何在单个键下对 JSON 数组中所有对象的键下存在的值进行分组？答案

【问题标题】：How do I group values present under a key in all objects in an array of JSON, under a single key?如何在单个键下对 JSON 数组中所有对象的键下存在的值进行分组？
【发布时间】：2020-05-19 12:19:10
【问题描述】：

我有一个 JSON 数组，例如：

[
   {user_id:1, name: "Person A", project: "Project A"},
   {user_id:1, name: "Person A", project: "Project B"},
   {user_id:2, name: "Person B", project: "Project A"},
   {user_id:2, name: "Person B", project: "Project C"},
   {user_id:3, name: "Person C", project: "Project D"}
]

我想转换这个数组，使一个人只有一个条目，并且它有一个值为 active_projects 的数组或他所有项目的值。基本上我想删除这个数组中的冗余。输出将是：

[
   {user_id:1, name: "Person A", active_projects: ["Project A","Project B"] },
   {user_id:2, name: "Person B", active_projects: ["Project A","Project C"] },
   {user_id:3, name: "Person C", active_projects: ["Project D"] }
]

什么是最干净和最好的方法？

【问题讨论】：

请添加您的尝试！
前几天你不是问过同样的问题吗？ stackoverflow.com/questions/61819398/…
@NinaScholz 实际上，我更改了数据检索模式以在单独的 SQL 查询中获取用户详细信息和项目，然后将它们合并到 O(n^2) 嵌套循环中。但这显然使我花费了额外的数据库查询和合并操作。如果我在单个查询中检索数据，它将如我的问题中所述。
@MoritzRoessler 如果您仔细查看 JSON 结构，这是一个不同的问题。

标签： javascript arrays json data-manipulation simplify

【解决方案1】：

一个简单的解决方案是首先使用 reduce 计算 user_ids 的映射。然后只需使用Object.values 将其变成一个数组。

const lkp = data.reduce((acc, {user_id, name, project}) => {
    acc[user_id] = acc[user_id] || {};
    acc[user_id].user_id = user_id;
    acc[user_id][name] = name;
    acc[user_id].active_projects = acc[user_id].active_projects || [];
    acc[user_id].active_projects.push(project);
    return acc;
}, {})

const arr = Object.values(lkp)

console.log(arr)

<script>
var data = [
   {user_id:1, name: "Person A", project: "Project A"},
   {user_id:1, name: "Person A", project: "Project B"},
   {user_id:2, name: "Person B", project: "Project A"},
   {user_id:2, name: "Person B", project: "Project C"},
   {user_id:3, name: "Person C", project: "Project D"}
];
</script>

【讨论】：

【解决方案2】：

你可以试试 JavaScript 的reduce 方法。

var data =[ {user_id:1, name: "Person A", project: "Project A"}, {user_id:1, name: "Person A", project: "Project B"}, {user_id:2, name: "Person B", project: "Project A"}, {user_id:2, name: "Person B", project: "Project C"}, {user_id:3, name: "Person C", project: "Project D"}];

result = Object.values(data.reduce((acc, {user_id, project, ...rest})=>{
  acc[user_id] =  acc[user_id] || { user_id, ...rest };
  acc[user_id].activeProject = acc[user_id].activeProject || [];
  acc[user_id].activeProject.push(project);
  return acc;
},{}));

console.log(result);

【讨论】：