How to sum duplicated values inside array in order

Question

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.

Try combining the arrays first, then filtering, then summing? — evolutionxbox, Sep 13 '21 at 14:01
Do the summing in an object whose keys are the names. Then get the object's keys and values to get the result array. — Barmar, Sep 13 '21 at 14:04
Do they really need to be in the original order? Shouldn't it be enough that the two result arrays are in consistent order with each other? — Barmar, Sep 13 '21 at 14:05
you want to only keep first occurrence of an element right? of among the duplicate values, you want minimum element or maximum element? — light1, Sep 13 '21 at 14:05
Can try searching for "JavaScript group by and sum" examples. Then apply those to your scenario — Shubham Periwal, Sep 13 '21 at 14:05
@0stone0 You're just handing out code, at best with a one-line explanation. Don't give people a free fish, teach them how to fish. At least that's how this website is supposed to work, afaik. — , Sep 13 '21 at 14:11
@0stone0 I would, but there's no appropriate close reason. And close votes don't stop people from posting cheap answers. — , Sep 13 '21 at 14:12

mplungjan · Accepted Answer · 2021-09-13T19:17:13.767

3

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)

edited Sep 13 '21 at 19:17

answered Sep 13 '21 at 14:07

mplungjan

169,008
28
173
236

2

I don't know. Your answer is by far the best! (I +1) – testing_22 Sep 13 '21 at 14:17
@mplungjan Yep like mine. Like your use of the ||. Cleaner than my use of an if statement. – Invizi Sep 13 '21 at 14:23

Nitheesh · Answer 2 · 2021-09-13T14:30:21.367

Please find your issue fixed below.

Logic

Create a new array to hold the sum of values called uniqueData.
While pushing data to uniqueValues push the value from array2 to uniqueData.
If the node already exist, update the sume value.

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

const uniqueValues = [];
const uniqueData = [];
for(var i in array1) {
  const index = uniqueValues.indexOf(array1[i]);
    if(index === -1){
      uniqueValues.push(array1[i]);
      uniqueData.push(array2[i]);
    } else {
      uniqueData[index] = (+uniqueData[index] + +array2[i]).toString()
    }
}

console.log(uniqueValues);
console.log(uniqueData);

Please find Array.reduce implementation of your requirement below. You can find the description as the code comment.

//Your dataset
const array1 = ['car', 'car', 'ball', 'piano', 'car'];
const array2 = ['2500', '1000', '400', '2500', '4500'];

// Array to hold the sum from array2
const uniqueData = [];

// Array to hold the aggrigate of array1
const uniqueValues = array1.reduce((acc, curr, itration) => {
  // acc: accumulator
  // curr: current node
  // itratiion: index of each node from array1

  // if the node is already present in accumulator
  // Dont push it to accumulator
  // Instead update the sume value in uniqueData array
  const index = acc.indexOf(curr);
  if(index === -1) {
    // Node is not there in accumulator
    // Then push to accumulator
    acc.push(curr);
    // Push the value in the index `itration` from `array2` to `uniqueData` array
    uniqueData.push(array2[itration])
  } else {
    // If the node is found update the data in uniqueData array
    // as the numeric sume of the value in that index and the value from array2
    uniqueData[index] = (+uniqueData[index] + +array2[itration]).toString()
  }
  return acc;
}, []); 
console.log(uniqueValues);
console.log(uniqueData);

score 2 · Answer 3 · edited Sep 13 '21 at 14:19

2

You can use a Map: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

If the number values are Strings like in your example, you also need to cast them to numbers first.

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

var map = new Map();

for (var i = 0; i < array1.length; i++) {
  var mapval = map.get(array1[i]);
  if (mapval == null) mapval = 0;
  mapval += array2[i];
  map.set(array1[i], mapval)
}

function logMapElements(value, key, map) {
  console.log(`m[${key}] = ${value}`);
}
map.forEach(logMapElements);

edited Sep 13 '21 at 14:19

mplungjan

169,008
28
173
236

answered Sep 13 '21 at 14:10

fire

149
1
5

@mplungjan the code works, but you can not do console.log(map). You can paste it into your browser console and see the results. I added a console.log to the example. – fire Sep 13 '21 at 14:18
Still it does not answer OPs question to set the two arrays – mplungjan Sep 13 '21 at 14:19

PeterKA · Answer 4 · 2021-09-14T15:48:27.223

(1) Use Array#reduce() and Object.assign() to build an object with unique keys (and values summed):

{ car: 8000, ball: 400, piano: 2500 }

(2) Use Object.keys() to get new array1:

[ 'car', 'ball', 'piano' ]

(3) Use Object.values() to get new array2:

[ 8000, 400, 2500 ]

DEMO 1

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

const result = array1.reduce((acc, cur, index) => Object.assign(acc, {
    [cur]: (acc[cur] || 0) + +array2[index]
}), {});

array1 = Object.keys(result);
array2 = Object.values(result);

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

You can also return an object literal directly in Array#reduce() as follows:

const result = array1.reduce((acc, cur, index) => ({
    ...acc,
    [cur]: ((acc[cur] || 0) + +array2[index])
}), {});

DEMO 2

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

const result = array1.reduce((acc,cur,index) => ({...acc,[cur]:((acc[cur] || 0) + +array2[index])}), {});

array1 = Object.keys(result);
array2 = Object.values(result);

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

score 1 · Answer 5 · edited Sep 13 '21 at 14:34

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

///Get unique values

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

var uniqueSums = [];

///Cycle through all items in original array

var _ind = 0;
array1.forEach(function(element) {

  //get associated value from second array 

  let _var = parseFloat(array2[_ind]);

  //Add value to total value in sum array

  let _uniqueInd = uniqueValues.indexOf(element);
  if (undefined != uniqueSums[_uniqueInd]) uniqueSums[_uniqueInd] = uniqueSums[_uniqueInd] + _var;
  else uniqueSums[_uniqueInd] = _var;
  _ind++;
});

//override org arrays
array1 = uniqueValues;
array2 = uniqueSums;

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

//will result:
//['car', 'ball', 'piano'] 
//['8000', '400', '2500']

I've created a snippet for you. Maybe you could improve your answer by adding some details. As shows here: [answer]; code-only answers are discouraged. — 0stone0, Sep 13 '21 at 14:26

David Biderman · Answer 6 · 2021-09-13T14:33:25.637

You can use a for each (this scenario applies if both arrays are same length)

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

const result = {};
array1.forEach((item, i) => {
  if (!result[item]) {
    result[item] = 0;
  }
  result[item] += Number(array2[i])
});

array1 = Object.keys(result); // ['car', 'ball', 'piano']
array2 = Object.values(result); // [8000, 400, 2500]

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

score 1 · Answer 7 · answered Sep 13 '21 at 15:15

Not exactly the best solution, but should work. I have used the map to create an index and add the values. It is a simple one.

let array1 = ['car', 'car', 'ball', 'piano', 'car', 'ball', 'piano'];
let array2 = ['2500', '1000', '400', '2500', '4500', '2500', '4500'];
const MapOfItems = new Map();
array1.forEach(function(item, index) {
  if (MapOfItems.has(item))
    MapOfItems.set(item, MapOfItems.get(item) + +array2[index]);
  else
    MapOfItems.set(item, +array2[index]);
});

console.log(MapOfItems);
console.log(MapOfItems.keys());
console.log(MapOfItems.values());

Invizi · Answer 8 · 2021-09-13T14:25:38.720

0

Here is how to do it with reduce.

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

const result = array1.reduce((a, word, index) => {
  if (!a[word]) a[word] = 0;
  a[word] += Number(array2[index]);
  return a
}, {});

const [keys, values] = [
  Object.keys(result),
  Object.values(result)
];

console.log({
  keys
}, {
  values
})

edited Sep 13 '21 at 14:25

answered Sep 13 '21 at 14:09

Invizi

1,270
1
7
7

That is only part one of [my answer](https://stackoverflow.com/a/69164140/295783) – mplungjan Sep 13 '21 at 14:12
@mplungjan No, it filters and adds them, so it does both parts. Run it and see. – Invizi Sep 13 '21 at 14:13
Please see my answer. OP said: _So the final result would be this:_ `array1 = ['car', 'ball', 'piano'] ` `array2 = ['8000', '400', '2500']` – mplungjan Sep 13 '21 at 14:14
@mplungjan Thought you would know how to destructure an object. I updated it anyway. – Invizi Sep 13 '21 at 14:21
Yes I know, but it was missing from yours and you are not rewriting array 1 and 2 - you cannot destruct if they are already defined – mplungjan Sep 13 '21 at 14:26

How to sum duplicated values inside array in order

8 Answers8