JavaScript SUM object values if the object's other values are the same

Question

I am pretty new to JS high array methods and I have an array of objects that contain cost categories and value like this:

[{category: "Bars", amount: 31231},
{category: "Transport", amount: 1297},
{category: "Utilities", amount: 12300},
{category: "Bars", amount: 2000},
{category: "Transport", amount: 2500},
{category: "Education", amount: 21321}]

My goal is to reduce this array and sum the 'amount' values like this:

[{category: "Bars", amount: 33231},  //31231+2000
{category: "Transport", amount: 3797}, //1297+2500
{category: "Utilities", amount: 12300},
{category: "Education", amount: 21321}]

I tried reduce() and and forEach(), but I could not really find a way to solve the issue. Thank you!

You can iterate thru the array and when categorys match add the amount to the first object and delete the latest one you found. — DoobyScooby
– DoobyScooby, Commented Oct 18, 2018 at 20:57

Juorder Gonzalez · Accepted Answer · 2018-10-18 20:58:59Z

You should use reduce method to do it, so you will iterate over the array with items and for each item you will ask if that category don't exist into the newObject then initialize it with 0 value and then sum up the amount.

var objects = [{category: "Bars", amount: 31231},
{category: "Transport", amount: 1297},
{category: "Utilities", amount: 12300},
{category: "Bars", amount: 2000},
{category: "Transport", amount: 2500},
{category: "Education", amount: 21321}];

var newObjectsMerged = objects.reduce((object, item) => {
  var category = item.category;
  var amount = item.amount;
  if (!object.hasOwnProperty(category)) {
    object[category] = 0;
  }
  
  object[category] += amount;
  return object;
}, {});

console.log("newObjectsMerged", newObjectsMerged);

Nina Scholz · Accepted Answer · 2018-10-18 21:01:57Z

You could reduce the array by taking finc for the object and update or add a new array to the result set.

var array = [{ category: "Bars", amount: 31231 }, { category: "Transport", amount: 1297 }, { category: "Utilities", amount: 12300 }, { category: "Bars", amount: 2000 }, { category: "Transport", amount: 2500 }, { category: "Education", amount: 21321 }],
    result = array.reduce((r, { category, amount }) => {
        var temp = r.find(o => o.category === category);
        if (temp) {
            temp.amount += amount;
        } else {
            r.push({ category, amount });
        }
        return r;
    }, []);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

AngelSalazar · Accepted Answer · 2018-10-18 20:58:08Z

var items = [{category: "Bars", amount: 31231},
{category: "Transport", amount: 1297},
{category: "Utilities", amount: 12300},
{category: "Bars", amount: 2000},
{category: "Transport", amount: 2500},
{category: "Education", amount: 21321}];


var itemsByName = items.reduce(function (map, item) {
  
  var summarizedItem = map.get(item.category);
  if (!summarizedItem) {
    summarizedItem = item;
  } else {
    summarizedItem.amount += item.amount;
  }
  
  map.set(item.category, summarizedItem);
  
  return map;
}, new Map());

console.log(Array.from(itemsByName.values()))

Charles Cavalcante · Accepted Answer · 2018-10-18 21:09:17Z

Try this:

var items = [{category: "Bars", amount: 31231},
{category: "Transport", amount: 1297},
{category: "Utilities", amount: 12300},
{category: "Bars", amount: 2000},
{category: "Transport", amount: 2500},
{category: "Education", amount: 21321}];

// get all categories names
var categories = items.map(item => item.category).filter((value, index, self) => self.indexOf(value) === index);

// create a new object with sum of amounts
var result = categories.map(item => { 
  return { 
     category: item, 
     amount: items.filter(c => c.category === item).reduce((accum, curr) => accum + curr.amount, 0) 
  } 
});

Leonid Pyrlia · Accepted Answer · 2018-10-18 21:15:06Z

A short ES6 version with Array.prototype.reduce and Object.keys:

const data = [{category: "Bars", amount: 31231},{category: "Transport", amount: 1297},{category: "Utilities", amount: 12300},{category: "Bars", amount: 2000},{category: "Transport", amount: 2500},{category: "Education", amount: 21321}];

const grouped = data.reduce((all, {category: c, amount: a}) =>
    ({...all, [c]: (all[c] || 0) + a }), {});

const result = Object.keys(grouped).map(k => ({category: k,amount: grouped[k] }));

console.log(result);

Collectives™ on Stack Overflow

JavaScript SUM object values if the object's other values are the same

5 Answers 5

1 Comment

Comments

Comments

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

Comments

Comments

Comments

Comments

Related