Regroup JSON array in JavaScript

Suppose, we have a JSON array of objects like this −

const arr = [
   {
      "id": "03868185",
      "month_10": 6,
   },
   {
      "id": "03870584",
      "month_6": 2,
   },
   {
      "id": "03870584",
      "month_7": 5,
   },
   {
      "id": "51295",
      "month_1": 1,
   },
   {
      "id": "51295",
      "month_10": 1,
   },
   {
      "id": "55468",
      "month_11": 1,
   }
];

Here, we can see that the same "id" property is being repeated in some objects. We are required to write a JavaScript function that takes in one such array that contains all the key/value pairs for a specific "id" property grouped in one single object.

Example

The code for this will be −

const arr = [
   {
      "id": "03868185",
      "month_10": 6,
   },
   {
      "id": "03870584",
      "month_6": 2,
   },
   {
      "id": "03870584",
      "month_7": 5,
   },
   {
      "id": "51295",
      "month_1": 1,
   },
   {
      "id": "51295",
      "month_10": 1,
   },
   {
      "id": "55468",
      "month_11": 1,
   }
];
const groupById = (arr = []) => {
   const map = {};
   const res = [];
   arr.forEach(el => {
      if(map.hasOwnProperty(el['id'])){
         const index = map[el['id']] - 1;
         const key = Object.keys(el)[1];
         res[index][key] = el[key];
      }
      else{
         map[el['id']] = res.push(el);
      }
   })
   return res;
};
console.log(groupById(arr));

Output

And the output in the console will be −

[
   { id: '03868185', month_10: 6 },
   { id: '03870584', month_6: 2, month_7: 5 },
   { id: '51295', month_1: 1, month_10: 1 },
   { id: '55468', month_11: 1 }
]