How to sum duplicated values inside array in order

I need some help to sum values inside an array in order

I have two arrays:

array1 = ['car', 'car', 'ball', 'piano', 'car'] 
array2 = ['2500', '1000', '400', '2500', '4500']

I’m using this code below to remove the duplicated values inside array1:

var uniqueValues = [];
for(var i in array1){
    if(uniqueValues.indexOf(array1[i]) === -1){
       uniqueValues.push(array1[i]);
    }
}

//returns ['car', 'ball', 'piano'] 

What I need is to sum the values of array2 using the order of array1, so I will have this result:

result = ['8000', '400', '2500']

So the final result would be this:

array1 = ['car', 'ball', 'piano'] 
array2 = ['8000', '400', '2500']

Any suggestion ? thank you.

Answer

Reduce will do the trick

NOTE Does JavaScript guarantee object property order?

let array1 = ['car', 'car', 'ball', 'piano', 'car'] 
let array2 = ['2500', '1000', '400', '2500', '4500']

const merged = array1.reduce((acc,cur,i) => {
  acc[cur] = (acc[cur] || 0) + +array2[i]; // add after casting to number
  return acc
},{})

console.log(merged)

array1 = Object.keys(merged)
array2 =  Object.values(merged)

console.log(array1)
console.log(array2)