merge values together in a 2d array

January 24, 2022

having a little bit of an issue trying to merge values in a 2d array.

For example:

const formatBids = 
 [
   [4444, 10000],
   [4444, 500],
   [4455, 500],
 ];

I want to sum up the 2nd param of the array if the first param are the same, so the end result being:

 [
   [4444, 10500],
   [4455, 500],
 ];

i have tried the following but its continually adding to itself producing the wrong results:

formatBids.map(bid => {
  const map = new Map([bid]);
  formatBids.forEach(arr => (arr[1] += map.get(arr[0]) ?? 0));
});

unsure the best way to tackle this. Ideas?

>Solution :

You could just use an Object as a sort of map and use the first item in an array as the key. Then you can convert it back to an Array using Object.entries(). Like so:

const formatBids = 
 [
   [4444, 10000],
   [4444, 500],
   [4455, 500],
 ];
 
const totals = {}

for (const bid of formatBids) {
  totals[bid[0]] = (totals[bid[0]] || 0) + bid[1];
}

console.log("as object:", totals, "as array:", Object.entries(totals));