JS count object match some same value

Question

i have a json like this:

 [{
          "semester":"1",
          "classification":"Excellent",
          "schoolYear":"2018"
       },
       {
          "semester":"2",
          "classification":"Intermediate",
          "schoolYear":"2018"
       },
       {
          "semester":"1",
          "classification":"Excellent",
          "schoolYear":"2018"
       },
       {
          "semester":"2",
          "classification":"Good",
          "schoolYear":"2017"
       },
       {
          "semester":"1",
          "classification":"Excellent",
          "schoolYear":"2017"
       },
       {
          "semester":"2",
          "classification":"Good",
          "schoolYear":"2017"
       },
       {
          "semester":"1",
          "classification":"Excellent",
          "schoolYear":"2017"
       },
       {
          "semester":"2",
          "classification":"Fail",
          "schoolYear":"2017"
       },
       {
          "semester":"1",
          "classification":"Good",
          "schoolYear":"2017"
       }]

and i want the output following this format by a function:

[
  {
    schoolYear: '2018',
    semesters: [
      {
        Excellent: 2,
        Good: 0,
        Intermediate: 0,
        Average: 0,
        Weak: 0,
        Fail: 0
      },
      {
        Excellent: 0,
        Good: 0,
        Intermediate: 1,
        Average: 0,
        Weak: 0,
        Fail: 0
      }
    ]
  },
  {
    schoolYear: '2017',
    semesters: [
      {
        Excellent: 3,
        Good: 1,
        Intermediate: 0,
        Average: 0,
        Weak: 0,
        Fail: 0
      },
      {
        Excellent: 0,
        Good: 2,
        Intermediate: 0,
        Average: 0,
        Weak: 0,
        Fail: 1
      }
    ]
  }
]

as you can see, the output is an array, each element in the array has 2 attributes, the schoolYear is a String, and the semesters is an array which contains 2 elements only, the first element at index 0 is for the "semester": "1" according to the input and the second element at index 1 is for the "semester": "2", of course.

i want to say thank to you to take time help me out, you can modify the code in this codesandbox demo here, once again, thank you very much and have a good day

Kerschbaumer Stefan · Accepted Answer · 2020-09-23 06:33:08Z

Here is an working example:

var obj = [
    {
        semester: "1",
        classification: "Excellent",
        schoolYear: "2018"
    },
    {
        semester: "2",
        classification: "Intermediate",
        schoolYear: "2018"
    },
    {
        semester: "1",
        classification: "Excellent",
        schoolYear: "2018"
    },
    {
        semester: "2",
        classification: "Good",
        schoolYear: "2017"
    },
    {
        semester: "1",
        classification: "Excellent",
        schoolYear: "2017"
    },
    {
        semester: "2",
        classification: "Good",
        schoolYear: "2017"
    },
    {
        semester: "1",
        classification: "Excellent",
        schoolYear: "2017"
    },
    {
        semester: "2",
        classification: "Fail",
        schoolYear: "2017"
    },
    {
        semester: "1",
        classification: "Good",
        schoolYear: "2017"
    }
];
const formatArray = (oldArray) => {

    const newArray = [];
    oldArray.forEach((oldEntry) => {
        let newObjIndex = newArray.findIndex((e) => e.schoolYear === oldEntry.schoolYear);
        if (newObjIndex === -1) {
            newArray.push({
                schoolYear: oldEntry.schoolYear
            });
            newObjIndex = newArray.length - 1;
        }
        if (!newArray[newObjIndex].semester) {
            newArray[newObjIndex].semester = [];
        }
        if (!newArray[newObjIndex].semester[oldEntry.semester]) {
            newArray[newObjIndex].semester[oldEntry.semester] = {};
        }
        newArray[newObjIndex].semester[oldEntry.semester][oldEntry.classification] = newArray[newObjIndex].semester[oldEntry.semester][oldEntry.classification]
            ? newArray[newObjIndex].semester[oldEntry.semester][oldEntry.classification] + 1
            : 1;
    });
    return newArray;
};
console.log(formatArray(obj));

thank you so much for the help, this is for my graduation thesis, you have just boosted my progress to finish it faster, lots of love and many thanks

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