在 Javascript 中重构 double for 循环

Question

在这种情况下是否可以将 for 循环的数量减少到只有一个？我需要根据“等级”属性对对象进行分组，无论输出的数据类型如何，即使您的解决方案迫使我重新开始也没关系。我现在对算法了解不多，所以我需要你的帮助来改进我的代码，因为我不允许在单个代码块中使用多个 for 循环。

var schools = {
    'SCHOOL_1':
    [
        // girls
        {id: '1', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'},
        {id: '2', school: 'SCHOOL_1', grade: 'A', message: 'Good work!'},
        {id: '3', school: 'SCHOOL_1', grade: 'A', message: 'Ok'},
        // boys
        {id: '4', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'},
        {id: '5', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'},
        {id: '6', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'},
        {id: '7', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'},
        {id: '8', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'},

    ],
    'SCHOOL_2':
    [
        // girls
        {id: '9', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '10', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '11', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '12', school: 'SCHOOL_2', grade: 'B', message: 'Good work!'},
        {id: '13', school: 'SCHOOL_2', grade: 'B', message: 'Nice!'},
        // boys
        {id: '14', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '15', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '16', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '17', school: 'SCHOOL_2', grade: 'B', message: 'Congratulations!'},
    ]
}

var result = [];

for (let school in schools) {
    // Group students by grade
    let studentsByGrade = GroupByProperty(schools[school], 'grade');
    // Second loop (I NEED TE REFACTOR THIS)
    for (let grade in studentsByGrade) {
        if (!result[grade]) result[grade] = [];
        result[grade].push(studentsByGrade[grade]);
    }
}

console.log('result',result);

function GroupByProperty(objectArray, property) {
    let result = objectArray.reduce((acc, obj) => {
       var key = obj[property];
       if (!acc[key]) acc[key] = [];
       acc[key].push(obj);
       return acc;
    }, {});

    return result;
}

Answer 1

通过组合Object.values 和Array.prototype.flat，您可以将此对象变成一个对象列表。

这样就可以了：

function GroupByProperty(objectArray, property) {
    let result = objectArray.reduce((acc, obj) => {
       var key = obj[property];
       if (!acc[key]) acc[key] = [];
       acc[key].push(obj);
       return acc;
    }, {});

    return result;
}

const byGrades = (schools) => 
  GroupByProperty (Object .values (schools) .flat(), 'grade')

var schools = {'SCHOOL_1': [{id: '1', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'}, {id: '2', school: 'SCHOOL_1', grade: 'A', message: 'Good work!'}, {id: '3', school: 'SCHOOL_1', grade: 'A', message: 'Ok'}, {id: '4', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'}, {id: '5', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'}, {id: '6', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'}, {id: '7', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'}, {id: '8', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'}], 'SCHOOL_2': [{id: '9', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'}, {id: '10', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'}, {id: '11', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'}, {id: '12', school: 'SCHOOL_2', grade: 'B', message: 'Good work!'}, {id: '13', school: 'SCHOOL_2', grade: 'B', message: 'Nice!'}, {id: '14', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'}, {id: '15', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'}, {id: '16', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'}, {id: '17', school: 'SCHOOL_2', grade: 'B', message: 'Congratulations!'}]}

console .log (byGrades (schools))

Answer 2

使用Object.values() flat() 和reduce() 的紧凑型解决方案，使用destructuring 实现并利用nullish coalescing operator。

const bygrade = Object.values(schools)
   .flat()
   .reduce((acc, o) => 
      (acc[o.grade] = [...acc[o.grade] ?? [], {...o}], acc), {});

var schools = {
    'SCHOOL_1':
    [
        // girls
        {id: '1', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'},
        {id: '2', school: 'SCHOOL_1', grade: 'A', message: 'Good work!'},
        {id: '3', school: 'SCHOOL_1', grade: 'A', message: 'Ok'},
        // boys
        {id: '4', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'},
        {id: '5', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'},
        {id: '6', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'},
        {id: '7', school: 'SCHOOL_1', grade: 'A', message: 'Congratulations!'},
        {id: '8', school: 'SCHOOL_1', grade: 'B', message: 'Good work!'},

    ],
    'SCHOOL_2':
    [
        // girls
        {id: '9', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '10', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '11', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '12', school: 'SCHOOL_2', grade: 'B', message: 'Good work!'},
        {id: '13', school: 'SCHOOL_2', grade: 'B', message: 'Nice!'},
        // boys
        {id: '14', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '15', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '16', school: 'SCHOOL_2', grade: 'A', message: 'Congratulations!'},
        {id: '17', school: 'SCHOOL_2', grade: 'B', message: 'Congratulations!'},
    ]
}

const bygrade = Object.values(schools).flat().reduce((acc, o) => (acc[o.grade] = [...acc[o.grade] ?? [], {...o}], acc), {});

console.log(bygrade);