How to group an array from given array of objects

Question

Does anyone know of to group an array from the given object then create a new array of objects? For example, I have an array of student objects:

Keep the array with its object and adding subject into an array please help me out find the below example.

var metaData = [
      {
          "student_name":'john'
          "student_class":'ten'
          "age":'16'
          "subject":'maths'
      },
      {
        "student_name":'john'
        "student_class":'ten'
        "age":'16'
        "subject":'science'
    },
    {
        "student_name":'john'
        "student_class":'ten'
        "age":'16'
        "subject":'arts'
    },{
        "student_name":'john'
        "student_class":'ten'
        "age":'16'
        "subject":'soical'
    },
    {
        "student_name":'john'
        "student_class":'ten'
        "age":'16'
        "subject":'biology'
    },
    
    {
        "student_name":'bellic'
        "student_class":'ninth'
        "age":'15'
        "subject":'general knowleadge'
    },
    {
      "student_name":'bellic'
      "student_class":'ninth'
      "age":'15'
      "subject":'games'
  },
  {
      "student_name":'bellic'
      "student_class":'ninth'
      "age":'15'
      "subject":'computer'
  },{
      "student_name":'bellic'
      "student_class":'ninth'
      "age":'15'
      "subject":'chemistry'
  },
  {
      "student_name":'bellic'
      "student_class":'ninth'
      "age":'15'
      "subject":'biology'
  },
  ]

I want to make a new array of subjects array inside new array of objects`

 var output:[
    {
        "student_name":'john'
        "student_class":'ten'
        "age":'16'
        "subject":['maths','science','arts','soical','biology']
    },
      {
        "student_name":'bellic'
        "student_class":'ninth'
        "age":'15'
        "subject":['general knowleadge','games','computer','chemistry','biology']
    }
  ]

I want to make it work with the function above.

reduce developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… is the function that will help you do this. — Gavin Bruce
– Gavin Bruce, Commented Mar 10, 2021 at 13:13

Jamiec · Accepted Answer · 2021-03-10 13:19:31Z

Using Object.values and Array.prototype.reduce this is fairly straightforward:

const result = Object.values(metaData.reduce( (acc,i) => {
    const key = i.student_name + i.student_class + i.age;
    if(!acc[key])
       acc[key] = {...i, subject: [i.subject] }
    else
       acc[key].subject.push(i.subject);
    return acc;
 },{}));

Live example:

var metaData = [
      {
          "student_name":'john',
          "student_class":'ten',
          "age":'16',
          "subject":'maths'
      },
      {
        "student_name":'john',
        "student_class":'ten',
        "age":'16',
        "subject":'science'
    },
    {
        "student_name":'john',
        "student_class":'ten',
        "age":'16',
        "subject":'arts'
    },{
        "student_name":'john',
        "student_class":'ten',
        "age":'16',
        "subject":'soical'
    },
    {
        "student_name":'john',
        "student_class":'ten',
        "age":'16',
        "subject":'biology'
    },
    
    {
        "student_name":'bellic',
        "student_class":'ninth',
        "age":'15',
        "subject":'general knowleadge'
    },
    {
      "student_name":'bellic',
      "student_class":'ninth',
      "age":'15',
      "subject":'games'
  },
  {
      "student_name":'bellic',
      "student_class":'ninth',
      "age":'15',
      "subject":'computer'
  },{
      "student_name":'bellic',
      "student_class":'ninth',
      "age":'15',
      "subject":'chemistry'
  },
  {
      "student_name":'bellic',
      "student_class":'ninth',
      "age":'15',
      "subject":'biology'
  },
  ]
  
 const result = Object.values(metaData.reduce( (acc,i) => {
    const key = i.student_name + i.student_class + i.age;
    if(!acc[key])
       acc[key] = {...i, subject: [i.subject] }
    else
       acc[key].subject.push(i.subject);
    return acc;
 },{}));
 
 console.log(result);

Krishnamraju K · Accepted Answer · 2021-03-10 13:36:09Z

FinalResult variable hold final value!!

     const finalResult = metaData.reduce((acc, item) =>{
     const isExist = acc.some(val => item.student_name  === val.student_name && item.student_class === val.student_class && item.age === val.age);

        if(isExist){
            return acc.map(arr => {
                if(item.student_name  === arr.student_name && item.student_class === arr.student_class && item.age === arr.age){
                    arr.subject = Array.isArray(arr.subject) ? [...arr.subject, item.subject] : [item.subject]
                }
                return arr;
            })
        }else{
          acc.push(item);
          return acc;
        }

    }, [])

    console.log(finalResult);

KooiInc · Accepted Answer · 2021-03-10 14:11:40Z

There a several possible solutions. This one reduces the original Array, using Array.reduce/filter/map.

const data = getData();
const groupedData = data
  .reduce((acc, record) =>
    !acc.find(v => v.student_name === record.student_name) ? [...acc,
      { ...record,
        subject: data
          .filter(v => v.student_name === record.student_name)
          .map(s => s.subject)
      }
    ] : acc, []);

console.log(groupedData);

function getData() {
  return [{
      "student_name": 'john',
      "student_class": 'ten',
      "age": '16',
      "subject": 'maths'
    },
    {
      "student_name": 'john',
      "student_class": 'ten',
      "age": '16',
      "subject": 'science',
    },
    {
      "student_name": 'john',
      "student_class": 'ten',
      "age": '16',
      "subject": 'arts'
    }, {
      "student_name": 'john',
      "student_class": 'ten',
      "age": '16',
      "subject": 'soical'
    }, {
      "student_name": 'john',
      "student_class": 'ten',
      "age": '16',
      "subject": 'biology'
    }, {
      "student_name": 'bellic',
      "student_class": 'ninth',
      "age": '15',
      "subject": 'general knowleadge'
    }, {
      "student_name": 'bellic',
      "student_class": 'ninth',
      "age": '15',
      "subject": 'games',
    }, {
      "student_name": 'bellic',
      "student_class": 'ninth',
      "age": '15',
      "subject": 'computer'
    }, {
      "student_name": 'bellic',
      "student_class": 'ninth',
      "age": '15',
      "subject": 'chemistry'
    }, {
      "student_name": 'bellic',
      "student_class": 'ninth',
      "age": '15',
      "subject": 'biology'
    },
  ];
}

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