How to perform a total summation from a loop?

Question

I have 2 arrays, users and questions, each has a nip_nim (ID). Questions array has thousands of rows each differentiate with nip_nim and role_id. How do I perform a total summation when the nip_nim in both array (users and questions) are the same?

I tried to push the total summation to a new array, but it's always replaced with the new one, and the summation value is the whole summation of array, not by individual nip_nim

export function hitungQuestions(questions, users) {
  users.forEach(function(uItem) {
    let P1 = 0;
    let P2 = 0;
    let P3 = 0;
    let P4 = 0;
    let data = [];
    let i = 0;

    questions.forEach(function(qItem) {

        if (qItem.nip_nim === uItem.nip_nim) {
            const role_id = qItem.role_id;

            // each question from 1-30
            const K001 = role_id === 1 ? qItem.K001 : 0;
            const K002 = role_id === 1 ? qItem.K002 : 0;
            const K003 = role_id === 1 ? qItem.K003 : 0;
            const K004 = role_id === 1 ? qItem.K004 : 0;
            const K005 = qItem.K005;
            const K006 = qItem.K006;
            const K007 = qItem.K007;
            const K008 = qItem.K008;
            const K009 = qItem.K009;
            const K010 = qItem.K010;
            const K011 = qItem.K011;
            const K012 = qItem.K012;
            const K013 = qItem.K013;
            const K014 = qItem.K014;
            const K015 = qItem.K015;
            const K016 = qItem.K016;
            const K017 = qItem.K017;
            const K018 = qItem.K018;
            const K019 = qItem.K019;
            const K020 = qItem.K020;
            const K021 = qItem.K021;
            const K022 = qItem.K022;
            const K023 = qItem.K023;
            const K024 = qItem.K024;
            const K025 = qItem.K025;
            const K026 = qItem.K026;
            const K027 = qItem.K027;
            const K028 = qItem.K028;
            const K029 = qItem.K029;
            const K030 = qItem.K030;

            // each question have different 'weight' based on role_id
            // except for C1
            const C1 = HitungC1(K001, K002, K003, K004);
            const C2 = HitungC2(role_id, K005, K006, K007);
            const C3 = HitungC3(role_id, K008, K009, K010);
            const C4 = HitungC4(role_id, K011, K012, K013);
            const C5 = HitungC5(role_id, K014, K015, K016, K017);
            const C6 = HitungC6(role_id, K018, K019, K020, K021, K022, K023);
            const C7 = HitungC7(role_id, K024, K025, K026, K027, K028, K029, K030);

            const TotalNilai = C1 / 4 + C2 / 3 + C3 / 3 + C4 / 3 + C5 / 4 + C6 / 6 + C7 / 7;

            if (role_id === 1) {
                P1 = P1 + TotalNilai;
            } else if (role_id === 2) {
                P2 = P2 + TotalNilai;
            } else if (role_id === 3) {
                P3 = P3 + TotalNilai;
            } else if (role_id === 4) {
                P4 = P4 + TotalNilai;
            }

            // if value > 20, return 'Very Good', and etc...
            const hasil = hitungHasil(TotalNilai);
      } 
      data.push({
          nip_nim: qItem.nip_nim,
          P1: P1,
          P2: P2,
          P3: P3,
          P4: P4
      });
    });
  });

}

Current output: With each iteration, it added a new array instead 'only' the final total value, and this is repeat as much as the number of user who has the same nip_nim (in my current database, it repeats 3 times out of 121 user)

    newArray(0)
    newArray(1)
    ...
    newArray(468)

Desired output

newArray = [
    {
       nip_nim: nip_nim_1,
       P1: P1, // a total of P1 from nip_nim_1
       P2: P2, // a total of P2 from nip_nim_1
       P3: P3, // a total of P3 from nip_nim_1
       P4: P4, // a total of P4 from nip_nim_1
       Total: Total // a total of P from nip_nim_1
    },
    {
       nip_nim: nip_nim_2,
       P1: P1, // a total of P1 from nip_nim_2
       P2: P2, // a total of P2 from nip_nim_2
       P3: P3, // a total of P3 from nip_nim_2
       P4: P4, // a total of P4 from nip_nim_2
       Total: Total // a total of P from nip_nim_1
    }, etc.
 ];

And what's not working with your current code? Where is your "Current output"? — Jack Bashford, Jan 13 '19 at 05:51
Possible duplicate of [Sum values from an Array in JavaScript](https://stackoverflow.com/questions/16057672/sum-values-from-an-array-in-javascript) — stealththeninja, Jan 13 '19 at 06:09
@stealththeninja thanks, but that's only possible after I 'normalize' the data into a single array like my answer below. My current workflow is to get the data from multiple dataset. — Eko Andri, Jan 13 '19 at 06:13

score 0 · Accepted Answer · answered Jan 13 '19 at 06:06

I've found a solution here https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce, by using group by method.

var people = [
  { name: 'Alice', age: 21 },
  { name: 'Max', age: 20 },
  { name: 'Jane', age: 20 }
];

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

var groupedPeople = groupBy(people, 'age');
// groupedPeople is:
// { 
//   20: [
//     { name: 'Max', age: 20 }, 
//     { name: 'Jane', age: 20 }
//   ], 
//   21: [{ name: 'Alice', age: 21 }] 
// }

With this method, I can just perform a summation in each own 'array' without having to juggling with different tables, and then push the final result to a new array.

How to perform a total summation from a loop?

1 Answers1