How to grouping data from array in js

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I have an array with different objects where each object is an classes. Looks like this:

sessions = [
      { session_id: 1, time: '09:00', student: { student_id: 1, name: 'Adi' }, class: { class_id: 1, name: 'A' } },
      { session_id: 2, time: '10:00', student: { student_id: 7, name: 'Dede' }, class: { class_id: 4, name: 'D' } },
      { session_id: 1, time: '09:00', student: { student_id: 3, name: 'Bayu' }, class: { class_id: 2, name: 'B' } },
      { session_id: 1, time: '09:00', student: { student_id: 2, name: 'Budi' }, class: { class_id: 1, name: 'A' } },
      { session_id: 2, time: '10:00', student: { student_id: 3, name: 'Maha' }, class: { class_id: 3, name: 'C' } },
    ];

I want to change the data to be like this, (grouping by session_id or time):

sessions = [
   {
     session_id: 1,
     time: '09:00',
     classes: [
       {
         class_id: 1,
         name: 'A',
         students: [
           { student_id: 1, name: 'Adi' },
           { student_id: 1, name: 'Budi' },
         ],
       },
       {
         class_id: 2,
         name: 'B',
         students: [
           { student_id: 3, name: 'Bayu' },
         ],
       },
     ],
   },
   {
     session_id: 2,
     time: '10:00',
     classes: [
       {
         class_id: 3,
         name: 'C',
         students: [
           { student_id: 6, name: 'Maha' },
         ],
       },
       {
         class_id: 4,
         name: 'D',
         students: [
           { student_id: 7, name: 'Dede' },
         ],
       },
     ],
   },
  ];

I'm tired of trying to solve it, because my javascript isn't that great. please help me to solve the code.

grouping mapping object arrays javascript
4 Answers

You can use lodash.groupBy. For example:

const sessions = [
    { session_id: 1, time: '09:00', student: { student_id: 1, name: 'Adi' }, class: { class_id: 1, name: 'A' } },
    { session_id: 2, time: '10:00', student: { student_id: 7, name: 'Dede' }, class: { class_id: 4, name: 'D' } },
    { session_id: 1, time: '09:00', student: { student_id: 3, name: 'Bayu' }, class: { class_id: 2, name: 'B' } },
    { session_id: 1, time: '09:00', student: { student_id: 2, name: 'Budi' }, class: { class_id: 1, name: 'A' } },
    { session_id: 2, time: '10:00', student: { student_id: 3, name: 'Maha' }, class: { class_id: 3, name: 'C' } },
];
const result = Object.entries(_.groupBy(sessions, 'session_id')).map(session => ({ session_id: Number(session[0]), time: session[1][0].time, classes: Object.entries(_.groupBy(session[1], s => s.class.class_id)).map(c => ({ class_id: Number(c[0]), name: c[1][0].class.name, students: c[1].map(x => ({ student_id: x.student.student_id, name: x.student.name })) })) }))
console.log(result)
<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.21/lodash.min.js"></script>

user_64160610

Try below snippet:

const sessions = [
      { session_id: 1, time: '09:00', student: { student_id: 1, name: 'Adi' }, class: { class_id: 1, name: 'A' } },
      { session_id: 2, time: '10:00', student: { student_id: 7, name: 'Dede' }, class: { class_id: 4, name: 'D' } },
      { session_id: 1, time: '09:00', student: { student_id: 3, name: 'Bayu' }, class: { class_id: 2, name: 'B' } },
      { session_id: 1, time: '09:00', student: { student_id: 2, name: 'Budi' }, class: { class_id: 1, name: 'A' } },
      { session_id: 2, time: '10:00', student: { student_id: 3, name: 'Maha' }, class: { class_id: 3, name: 'C' } },
    ];

const newSessions = sessions.reduce((acc, session)=> {
    const sessionIndex = acc.findIndex(item => item.session_id == session.session_id);
    if(sessionIndex > -1){
        updateSessionClasses(acc[sessionIndex], session)
    }else {
        acc.push({ session_id: session.session_id, time: session.time, classes: [{...session.class, students: [session.student]}]  })
    };
    return acc;
}, []);

function updateSessionClasses(storedSession, session){
    const classIndex = storedSession.classes.findIndex(c => c.class_id == session.class.class_id);
    if(classIndex > -1){
      storedSession.classes[classIndex].students.push(session.student)
    }else {
       storedSession.classes.push({...session.class, students: [session.student]}) 
    }
}

console.log(newSessions)

user_119779290

We can use Array.reduce(), grouping by session_id, then adding class and student to each session if not present:

const sessions = [
  { session_id: 1, time: '09:00', student: { student_id: 1, name: 'Adi' }, class: { class_id: 1, name: 'A' } },
  { session_id: 2, time: '10:00', student: { student_id: 7, name: 'Dede' }, class: { class_id: 4, name: 'D' } },
  { session_id: 1, time: '09:00', student: { student_id: 3, name: 'Bayu' }, class: { class_id: 2, name: 'B' } },
  { session_id: 1, time: '09:00', student: { student_id: 2, name: 'Budi' }, class: { class_id: 1, name: 'A' } },
  { session_id: 2, time: '10:00', student: { student_id: 3, name: 'Maha' }, class: { class_id: 3, name: 'C' } },
];

const result = Object.values(sessions.reduce((acc, { session_id, time, student, ['class']: { class_id, name }}) => {
    acc[session_id] = acc[session_id] || { session_id, time, classes: [] };
    let cl = acc[session_id].classes.find(c => c.class_id === class_id);
    if (!cl) {
        cl = { class_id, name, students: []}
        acc[session_id].classes.push(cl); 
    } 
    cl.students.push(student);
    return acc;
}, {}));

console.log('Result:', result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

user_72372240 

sessions = [
  { session_id: 1, time: '09:00', student: { student_id: 1, name: 'Adi' }, class: { class_id: 1, name: 'A' } },
  { session_id: 2, time: '10:00', student: { student_id: 7, name: 'Dede' }, class: { class_id: 4, name: 'D' } },
  { session_id: 1, time: '09:00', student: { student_id: 3, name: 'Bayu' }, class: { class_id: 2, name: 'B' } },
  { session_id: 1, time: '09:00', student: { student_id: 2, name: 'Budi' }, class: { class_id: 1, name: 'A' } },
  { session_id: 2, time: '10:00', student: { student_id: 3, name: 'Maha' }, class: { class_id: 3, name: 'C' } },
];

const studentsRedused = sessions.reduce((acc, { session_id, student, class: { class_id } }) => {
  const session_class = `${session_id}-${class_id}`;
  acc[session_class] = acc[session_class]
    ? [...acc[session_class], { ...student }]
    : [{ ...student }]
  return acc;
}, {});

const classesRedused = sessions.reduce((acc, { session_id, class: { class_id, name } }) => {
  const needAddClass = acc[session_id] ? !acc[session_id].some((o) => o.class_id === class_id) : true
  if (needAddClass) {
    acc[session_id] = acc[session_id]
      ? [...acc[session_id], { class_id, name }]
      : [{ class_id, name }]
  }
  return acc;
}, {});

const reduced = sessions.reduce((acc, { session_id, time, class: { class_id, name } }) => {
  const classes = classesRedused[session_id].map((objClass) => {
    const session_class = `${session_id}-${objClass.class_id}`;
    return  { ...objClass, students: studentsRedused[session_class] }
  });
  acc[session_id] = { session_id, time, classes }
  return acc;
}, {});

const result = Object.values(reduced);

console.dir(result, {depth: null});
.as-console-wrapper { max-height: 100% !important; top: 0; }

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