Array formations

Issue

Here i have a array of objects. I want the each grade as seperate array and inside the array i want the grade based section and subjects.

If teacher is taking a grade i want the schema as which grade they take and what section, inside that what subject they are taking.

var user = [
  RowDataPacket { grade_id: 3, subject_id: 3, section_id: 747 },
  RowDataPacket { grade_id: 4, subject_id: 3, section_id: 748 },
  RowDataPacket { grade_id: 5, subject_id: 3, section_id: 749 },
  RowDataPacket { grade_id: 6, subject_id: 3, section_id: 750 },
  RowDataPacket { grade_id: 7, subject_id: 3, section_id: 751 },
  RowDataPacket { grade_id: 8, subject_id: 3, section_id: 752 },
  RowDataPacket { grade_id: 7, subject_id: 4, section_id: 751 }
]

Desired / target schema

let gradeDetails = [{
  grade_id: 3,
  section_details: [{
    section_id: 747,
    subject_details: [{subject_id: 3}]
  }]
}, {
  .
  .
  .
}, {
  grade_id: 7
  section_details: [{
    section_id: 751,
    subject_details: [
      {subject_id: 3},
      {subject_id: 4}
    ]
  }]
}, {
  grade_id: 8,
  section_details: [{
    section_id: 752,
    subject_details: [{subject_id: 3}]
  ]}
}];

Solution

The below code snippet may be one way to achieve the desired result:

Code Sample

const getGradeDetailsArray = (arr = user) => {
  const resultArr = [];
  for (const grade of (new Set(arr.map(obj => obj.grade_id)))) {
    const resObj = {
        grade_id: grade,
      section_details: arr.filter(
        obj => obj.grade_id === grade
        ).map(
        obj => ({
            section_id: obj.section_id,
          subject_details: [{ subject_id: obj.subject_id }]
          })
        )
    };
    resultArr.push(resObj)
  };
  return resultArr;
};

Explanation

• Initialize the result as an empty-array named resultArr
• Obtain unique grade_ids by using new Set() and iterate over each grade
• For each grade, construct an object to be pushed to the result
• grade_id is set to grade
• section_details is set as an array filtered by matching grade_id
• subect_details is an array with exactly one element (ie, the subject_id).
• Return the resultArr

Code Snippet

const user = [
    { grade_id: 3, subject_id: 3, section_id: 747 },
  { grade_id: 4, subject_id: 3, section_id: 748 },
  { grade_id: 5, subject_id: 3, section_id: 749 },
  { grade_id: 6, subject_id: 3, section_id: 750 },
  { grade_id: 7, subject_id: 3, section_id: 751 },
  { grade_id: 8, subject_id: 3, section_id: 752 },
  { grade_id: 7, subject_id: 4, section_id: 751 },
];

const getGradeDetailsArray = (arr = user) => {
  const resultArr = [];
  for (const grade of (new Set(arr.map(obj => obj.grade_id)))) {
    const resObj = {
        grade_id: grade,
      section_details: arr.filter(
        obj => obj.grade_id === grade
        ).map(
        obj => ({
            section_id: obj.section_id,
          subject_details: [{ subject_id: obj.subject_id }]
          })
        )
    };
    resultArr.push(resObj)
  };
  return resultArr;
};

console.log(getGradeDetailsArray());

const newGetGradeDetails = (arr = user) => (
    Object.entries(
    arr.reduce((fin, itm) => ({
      ...fin,
      [itm.grade_id]: {
        ...fin[itm.grade_id],
        [itm.section_id]: {
          ...(fin && fin[itm.grade_id] && fin[itm.grade_id][itm.section_id]
                ? fin[itm.grade_id][itm.section_id]
                : {}
             ),
          subjects: [
            ...(fin && fin[itm.grade_id] &&
                fin[itm.grade_id][itm.section_id] &&
                fin[itm.grade_id][itm.section_id].subjects &&
                Array.isArray(fin[itm.grade_id][itm.section_id].subjects)
                ? fin[itm.grade_id][itm.section_id].subjects
                : []
               ),
            itm.subject_id
          ]
        }
      }
    }) ,{})
  ).map(([kg, vg]) => ({
    grade_id: kg,
    section_details: Object.entries(vg).map(([kse, vse]) => ({
        section_id: kse,
      subject_details: vse.subjects.map(su => ({
        subject_id: su
      }))
    }))
  }))
);

console.log('\n\tUpdated as per comments noted below\n\n', newGetGradeDetails());

Edit: Added new method to account for changes requested on comments below.

Answered By - jsN00b