How to remove duplicate elements in two dimensional array by adding the values

I have a two dimensional array as such

const arr = [[1664164800000,38],[1669006800000,11],[1669611600000,4],[1669611600000,12],[1670216400000,8]]

and I would like to filter the duplicate keys and add the values as such

[[1664164800000,38],[1669006800000,11],[1669611600000,16],[1670216400000,8]]

Is it possible to achieve?

>Solution :

You can use reduce for this purpose

arr.reduce((acc, [key, value]) => {
  const dict = acc[1];
  if (!dict[key]) {
    const item = [key, value]; // add new item (copy value to prevent mutation of passed input)
    acc[0].push(item);
    dict[key] = item;
  } else {
    const [_, prevValue] = dict[key];
    dict[key][1] = prevValue + value; // modify/mutate item value
  }
  return acc;
}, [[], {}])[0];