如何格式化JSON对象数组（JavaScript）

Question

I am struggling with a tough requirement where I don't know how to deal with

I received one Array as below:

[{
    "student": "21_A_1",
    "sport": "badminton"
}, {
    "student": "21_C_1",
    "sport": "badminton"
}, {
    "student": "21_A_2",
    "sport": "badminton"
}, {
    "student": "21_B_1",
    "sport": "football"
}, {
    "student": "21_A_2",
    "sport": "football"
}]

Requirement: convert it to an array with format :

[{
    "student": "21_A_1",
    "sport": ["badminton"]
}, {
    "student": "21_C_1",
    "sport": ["badminton"]
}, {
    "student": "21_A_2",
    "sport": ["badminton","football"]
}, {
    "student": "21_B_1",
    "sport": ["football"]
}]

I found that lodash library has a feature "group by" returned quite closed result but not as expectation:

_.groupBy(array, 'student');

Result:

{
    "21_A_1": [{
        "student": "21_A_1",
        "sport": "badminton"
    }],
    "21_C_1": [{
        "student": "21_C_1",
        "sport": "badminton"
    }],
    "21_A_2": [{
        "student": "21_A_2",
        "sport": "badminton"
    }, {
        "student": "21_A_2",
        "sport": "football"
    }],
    "21_B_1": [{
        "student": "21_B_1",
        "sport": "football"
    }]
}

Any suggestion is very appreciated.

Answer 1

We can use '.reduce' function of array and aggregate result as below

 var test = [{ "student": "21_A_1", "sport": "badminton" }, { "student": "21_C_1", "sport": "badminton" }, { "student": "21_A_2", "sport": "badminton" }, { "student": "21_B_1", "sport": "football" }, { "student": "21_A_2", "sport": "football" }] const result = test.reduce((res,x)=>{ res[x.student] = res[x.student] || { student:x.student,sport:[]} res[x.student].sport.push(x.sport) return res; },{}) console.log(result) 

Answer 2

You need to map the grouped items with their sport propery and build new objects with the grouping informations.

 var array = [{ student: "21_A_1", sport: "badminton" }, { student: "21_C_1", sport: "badminton" }, { student: "21_A_2", sport: "badminton" }, { student: "21_B_1", sport: "football" }, { student: "21_A_2", sport: "football" }], grouped = _(array) .groupBy('student') .map((group, student) => ({ student, sport: _.map(group, 'sport') })) .value(); console.log(grouped); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script> 

Answer 3

Using Array.prototype.reduce() combined with Object.values() :

 const data = [{"student": "21_A_1","sport": "badminton"}, {"student": "21_C_1","sport": "badminton"}, {"student": "21_A_2","sport": "badminton"}, {"student": "21_B_1","sport": "football"}, {"student": "21_A_2","sport": "football"}]; const result = Object.values( data.reduce((a, c) => ((a[c.student] = a[c.student] || {student: c.student, sport: []}).sport.push(c.sport), a), {}) ); console.log(result);