JavaScript sum values if duplicate value in object

Question

I have an object:

const transaction = [{
  created: 1200,
  amount: 200
},{
  created: 1200,
  amount: 400
},{
  created: 1400,
  amount: 400
},{
  created: 1400,
  amount: 300
},{
  created: 1500,
  amount: 100
}]

Everytime created has the same value I want to sum the amount's of the objects. So for example created: 1200 would have an amount of: 600 in total, because multiple created's where at 1200 so the amount got summed up.

This may be helpful: https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects — Anis R., Aug 24 '20 at 19:08
@RobinZigmond well I have tried using `Array.prototype.reduce` to sum up the values. But I can't figure out the logic to only use it on the appriopriate object. — Ezrab_, Aug 24 '20 at 19:09
@Ezrab_ `reduce` sounds like the right idea - can you share your attempt? — Robin Zigmond, Aug 24 '20 at 19:19
Use an if statement in the callback you use in `reduce`, so you check for the value of `created` before summing. — Terry, Aug 24 '20 at 19:37

Saadi Toumi Fouad · Accepted Answer · 2020-08-24T19:44:33.690

Here is a simple solution, note that I coded it fast so it can be optimized later

const transaction = [{
  created: 1200,
  amount: 200
},{
  created: 1200,
  amount: 400
},{
  created: 1400,
  amount: 400
},{
  created: 1400,
  amount: 300
},{
  created: 1500,
  amount: 100
}];
// accepts an array of objects
function sumObj(objArr) {
  // an object to store the `created` and `amount` as key=>value
  var newObj = {};
  // loop over the objects in the array
  objArr.forEach(function(obj) {
    // if the key is present in `newObj` then we need to add the amount to it's value
    if(obj.created in newObj) {
      newObj[obj.created] += obj.amount;
    }else {
      // else just add the key and the amount as value
      newObj[obj.created] = obj.amount;
    }
  });
  //  create an array to store the final objects
  var arr = [];
  // loop over the properties in `newObj`
  for(var prop in newObj) {
    // push an object each time
    arr.push({created: Number(prop), amount: newObj[prop]});
  }
  // return the final result
  return arr;
}
// log it to see the output
console.log(sumObj(transaction));

Note: I have noticed that each object in the array is sorted according to .created so I came up with another solution, note that if the objects are not always sorted then use the first solution instead

const transaction = [{
  created: 1200,
  amount: 200
},{
  created: 1200,
  amount: 400
},{
  created: 1400,
  amount: 400
},{
  created: 1400,
  amount: 300
},{
  created: 1500,
  amount: 100
}];
// accepts an array of objects
function sumObj(objArr) {
  // create an array to store the objects
  var newArr = [];
  // loop over the objects in the array
  objArr.forEach(function(obj, ind, arr) {
    // so since we check for the current object against the next one
    // we need to check when there is no next one to avoid errors
    // the idea is to check if the current object has the same .created
    // of the next object then add the amount to the next object
    // else check if this is the last object then just push it to the array
    // or if the current object has a different .created value then
    // just push it
    if(ind === arr.length - 1 || obj.created !== arr[ind + 1].created) {
      newArr.push(obj);
    }else {
      arr[ind + 1].amount += obj.amount;
    }
  });
  // return the result
  return newArr;
}
// print the result
console.log(sumObj(transaction));

score 0 · Answer 2 · answered Aug 24 '20 at 20:04

const transaction = [{
  created: 1200,
  amount: 200
},{
  created: 1200,
  amount: 400
},{
  created: 1400,
  amount: 400
},{
  created: 1400,
  amount: 300
},{
  created: 1500,
  amount: 100
}];

function getComputedTransaction(transHistory) {
  let tempHistory = [];
  transHistory.forEach((item)=>{
    let noMatch = true; // temp created match conditioner
    if(tempHistory.length > 0) {
      tempHistory.forEach((tempItem, i)=>{
        if(item.created === tempItem.created) {
          tempHistory[i].amount += item.amount;
          noMatch = !noMatch; // make noMatch = false
        }
      });
    }
    return (noMatch) ? tempHistory.push(item) : null;
  });
  return tempHistory;
}

console.log(getComputedTransaction(transaction));

JavaScript sum values if duplicate value in object

2 Answers2