Summing all the unique values of an array - JavaScript

Let’s say, we are required to write a JavaScript function that takes in an array of numbers with duplicate entries and sums all the duplicate entries to one index.

For example −

If the input array is −

const input = [1, 3, 1, 3, 5, 7, 5, 4];

Then the output should be −

const output = [2, 6, 7, 10, 4];

That means all the duplicate ones are summed to index 0 and all the duplicate threes are summed to index 1 and so on.

Example

Following is the code −

const input = [1, 3, 1, 3, 5, 7, 5, 4];
const mergeDuplicates = arr => {
   const map = arr.reduce((acc, val) => {
      if(acc.has(val)){
         acc.set(val, acc.get(val) + 1);
      }else{
         acc.set(val, 1);
      };
      return acc;
   }, new Map());
   return Array.from(map, el => el[0] * el[1]);
};
console.log(mergeDuplicates(input));

Output

This will produce the following output in console −

[ 2, 6, 10, 7, 4 ]