Grouping an Array and Counting items creating new array based on Groups in JavaScript

Suppose, we have an array of objects like this −

const arr = [
   { region: "Africa", fruit: "Orange", user: "Gary" },
   { region: "Africa", fruit: "Apple", user: "Steve" },
   { region: "Europe", fruit: "Orange", user: "John" },
   { region: "Europe", fruit: "Apple", user: "bob" },
   { region: "Asia", fruit: "Orange", user: "Ian" },
   { region: "Asia", fruit: "Apple", user: "Angelo" },
   { region: "Africa", fruit: "Orange", user: "Gary" }
];

We are required to write a JavaScript function that takes in one such array. The function should prepare a new array of objects that groups the data based on the "area" property of objects.

The function should also keep a count of the unique users for a particular area.

Therefore, for the above array, the output should look like −

const output = [
   {
      "region": "Africa",
      "count": 2
   },
   {
      "region": "Europe",
      "count": 2
   },
   {
      "region": "Asia",
      "count": 2
   }
];

Example

The code for this will be −

const arr = [
   { region: "Africa", fruit: "Orange", user: "Gary" },
   { region: "Africa", fruit: "Apple", user: "Steve" },
   { region: "Europe", fruit: "Orange", user: "John" },
   { region: "Europe", fruit: "Apple", user: "bob" },
   { region: "Asia", fruit: "Orange", user: "Ian" },
   { region: "Asia", fruit: "Apple", user: "Angelo" },
   { region: "Africa", fruit: "Orange", user: "Gary" }
];
const groupByArea = (arr = []) => {
   const res = [];
   arr.forEach(el => {
      let key = [el.region, el.user].join('|');
      if (!this[el.region]) {
         this[el.region] = { region: el.region, count: 0 };
         res.push(this[el.region]);
      };
      if (!this[key]) {
         this[key] = true;
         this[el.region].count++;
      };
   }, Object.create(null));
   return res;
}
console.log(groupByArea(arr));

Output

And the output in the console will be −

[
   { region: 'Africa', count: 2 },
   { region: 'Europe', count: 2 },
   { region: 'Asia', count: 2 }
]