Imagine I have an array:

let profile = [
{student: "A", english: 80, maths: 80},
{student: "A", english: 70, maths: 60},
{student: "B", english: 50, maths: 50},
{student: "B", english: "--", maths: 60},
...
]

I want to get two sets of array regarding the average.

1. The average scores of each subject of each student (Expected output:)

[{student: "A", english: 75, maths: 70},
{student: "B", english: 50, maths: 55}]

2. The average scores of every subject of each student (Expected output:)

[{student: "A", average: 72.5},
{student: "B", average: 53.3}]

How can I code it? Thank you very much

CodePudding user response：

I'm not sure but how did you get the average of student B to be 53.3 on the 2nd array...

Check my code below, i got 52.5 instead.

let profile = [
{student: "A", english: 80, maths: 80},
{student: "B", english: 50, maths: 50},
{student: "A", english: 70, maths: 60},
{student: "B", english: "--", maths: 60}
]


//sort by student
profile.sort((a, b) => a.student.localeCompare(b.student));


const studentsCount = profile.reduce((pre, cur, index) => {
    let find = profile.findIndex((e, _index) => _index > index && e.student === cur.student);
    if (find == -1) {
        return pre   1;
    } else return pre;
}, 0);


//stage 1
let curProfile = profile[0], startIndex, endIndex, _profile = [], maths, english, noScoreMaths, noScoreEnglish;
for (let i = 0; i < studentsCount; i  ) {
    startIndex = profile.findIndex(p => p.student === curProfile.student);
    endIndex = profile.findLastIndex(p => p.student === curProfile.student);
    noScoreMaths = 0, noScoreEnglish = 0;

    for (let j = startIndex; j <= endIndex; j  ) {
        if (isNaN(parseInt(profile[j].maths))) noScoreMaths  ;
        if (isNaN(parseInt(profile[j].english))) noScoreEnglish  ;
        
        if (j === startIndex) {
            maths = isNaN(parseInt(profile[j].maths)) ? 0 : profile[j].maths;
            english = isNaN(parseInt(profile[j].english)) ? 0 : profile[j].english;
        } else {
            maths  = isNaN(parseInt(profile[j].maths)) ? 0 : profile[j].maths;
            english  = isNaN(parseInt(profile[j].english)) ? 0 : profile[j].english;
            
            if (j === endIndex) {
                maths = parseFloat((maths / (endIndex - startIndex   1 - noScoreMaths)).toFixed(1));
                english = parseFloat((english / (endIndex - startIndex   1 - noScoreEnglish)).toFixed(1));
            }

            _profile.push({
                student: curProfile.student,
                maths,
                english
            });

            curProfile = profile[j   1];
            noScoreMaths = 0;
            noScoreEnglish = 0;
        }
    }
}

//stage 2
let __profile = [];

for (let i = 0; i < _profile.length; i  ) {
    let avgScore = parseFloat(((_profile[i].maths   _profile[i].english) / 2).toFixed(1));
    __profile.push({ student: _profile[i].student, average: avgScore });
}

console.log(_profile);
console.log(__profile);

CodePudding user response：

You could use a grouping for the students' scores and get the avarage on each subject and then get the average of each student.

const
    profile = [{ student: "A", english: 80, maths: 80 }, { student: "A", english: 70, maths: 60 }, { student: "B", english: 50, maths: 50 }, { student: "B", english: "--", maths: 60 }],
    result1 = Object
        .values(profile.reduce((r, { student, ...o }) => {
            r[student] ??= { student };
            Object
                .entries(o)
                .forEach(([k, v]) => {
                    if (isNaN(v)) return;
                    r[student][k] ??= { total: 0, count: 0 };
                    r[student][k].total  = v;
                    r[student][k].count  ;
                });
            return r;
        }, {}))
        .map(({ student, ...o }) => ({
            student,
            ...Object.fromEntries(Object.entries(o).map(([k, { total, count }]) => [k, total / count]))
        })),
    result2 = result1.map(({ student, ...o }) => {
        const values = Object.values(o);
        return {
            student,
            average: values.reduce((a, b) => a   b, 0) / values.length
        };
    });

console.log(result1);
console.log(result2);

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