Counting duplicates and aggregating array of objects in JavaScript

Suppose, we have an array of objects like this −

const arr = [
   {
      "Country": "BR",
      "New Lv1−Lv2": "#N/A"
   },
   {
      "Country": "BR",
      "New Lv1−Lv2": "#N/A"
   },
   {
      "Country": "",
      "New Lv1−Lv2": "test"
   }];

We are required to write a JavaScript function that takes in one such array of objects. The function creates and return a new array in which no objects are repeated (by repeated we mean objects having same value for "Country" property.)

Moreover, the function should assign a count property to each object that represents the number of times they appeared in the original array.

Example

The code for this will be −

const arr = [
   {
      "Country": "BR",
      "New Lv1−Lv2": "#N/A"
   },
   {
      "Country": "BR",
      "New Lv1−Lv2": "#N/A"
   },
   {
      "Country": "",
      "New Lv1−Lv2": "test"
   }];
   const convert = (arr) => {
      const res = {};
      arr.forEach((obj) => {
         const key = `${obj.Country}${obj["New Lv1−Lv2"]}`;
         if (!res[key]) {
            res[key] = { ...obj, count: 0 };
         };
         res[key].count += 1;
      });
   return Object.values(res);
};
console.log(convert(arr));

Output

And the output in the console will be −

[
   { Country: 'BR', 'New Lv1-Lv2': '#N/A', count: 2 },
   { Country: '', 'New Lv1-Lv2': 'test', count: 1 }
]

AmitDiwan

Published on 23-Nov-2020 11:51:33