JavaScript中新对象数组中数组对象属性值的总和
假设我们有一个对象数组，其中包含有关某些学生及其分数的数据，如下所示：
const arr = [
{ subject: 'Maths', marks: '40', noOfStudents: '5' },
{ subject: 'Science', marks: '50', noOfStudents: '16' },
{ subject: 'History', marks: '35', noOfStudents: '23' },
{ subject: 'Science', marks: '65', noOfStudents: '2' },
{ subject: 'Maths', marks: '30', noOfStudents: '12' },
{ subject: 'History', marks: '55', noOfStudents: '20' },
];我们需要编写一个包含一个这样的数组的JavaScript函数。
该功能应根据对象的“主题”属性消除冗余条目。此外，该功能应在单个对象中添加唯一对象的所有分数，而不添加学生数。
因此，对于上述数组，输出应类似于-
const output = [
{ subject: 'Maths', marks: '70', noOfStudents: '17' },
{ subject: 'Science', marks: '115', noOfStudents: '18' },
{ subject: 'History', marks: '95', noOfStudents: '43' },
];示例
为此的代码将是-
const arr = [
{ subject: 'Maths', marks: '40', noOfStudents: '5' },
{ subject: 'Science', marks: '50', noOfStudents: '16' },
{ subject: 'History', marks: '35', noOfStudents: '23' },
{ subject: 'Science', marks: '65', noOfStudents: '2' },
{ subject: 'Maths', marks: '30', noOfStudents: '12' },
{ subject: 'History', marks: '55', noOfStudents: '20' },
];
const groupBySubject = (arr = []) => {
const map = {};
let res = [];
res = arr.reduce((acc, val) => {
const { subject, marks, noOfStudents } = val;
const { length: l } = acc;
if(map.hasOwnProperty(subject)){
acc[map[subject]]['marks'] = +marks;
acc[map[subject]]['noOfStudents'] = +noOfStudents;
}
else{
map[subject] = l;
acc.push({
subject: subject,
marks: +marks,
noOfStudents: +noOfStudents
});
};
return acc;
}, []);
return res;
};
console.log(groupBySubject(arr));输出结果
控制台中的输出将是-
[
{ subject: 'Maths', marks: 30, noOfStudents: 12 },
{ subject: 'Science', marks: 65, noOfStudents: 2 },
{ subject: 'History', marks: 55, noOfStudents: 20 }
]