What is the best way to reduce and merge a collection of objects

user_9532034 0
Viewed 74

So I reached a dilemma this week while trying to solve what seemed to be an easy problem, but I was wrong.

Sample code:

let arr = [
  { id: 'ae0123', cost: 100.00, orders: 5 },
  { id: 'ae0123', cost: 50.00, orders: 5 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
]

So the problem was being able to map through the array and merge/sum the values if their unique identifiers match.

Any suggestions?

End result would look something like this:

[
  { id: 'ae0123', cost: 150.00, orders: 10 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
]

Now of course the real application will not have statically typed ids, but they were written into this example. So please take that into consideration.

Thanks in advance!

object collections arrays javascript
7 Answers

You can use a Map to store objects by id, and add the values if it already exists in it:

let arr = [
  { id: 'ae0123', cost: 100.00, orders: 5 },
  { id: 'ae0123', cost: 50.00, orders: 5 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
];
let map = {};
for(let i = 0; i < arr.length; i++){
     let item = arr[i];
     if(map[item.id]){
          map[item.id].cost += item.cost;
          map[item.id].orders += item.orders;
     }else{
          map[item.id] = item;
     }
}
console.log(Object.values(map));

user_74863130

You could take an object for grouping and an array for adding the wanted properties.

let array = [{ id: 'ae0123', cost: 100.00, orders: 5 }, { id: 'ae0123', cost: 50.00, orders: 5 }, { id: 'ae4321', cost: 75.00, orders: 1 }],
    result = Object.values(array.reduce((r, o) => {
        if (r[o.id]) {
            ['cost', 'orders'].forEach(k => r[o.id][k] += o[k]);
        } else {       
            r[o.id] = { ...o };
        }
        return r;
    }, {}));

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

user_14476750

Create a new array

For each item, if it already exists then add the cost and orders, else add it to the array.

let arr = [
  { id: 'ae0123', cost: 100.00, orders: 5 },
  { id: 'ae0123', cost: 50.00, orders: 5 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
]

let newArr = []

arr.forEach(item => {
  let existingItem = newArr.find(x => x.id == item.id);
  if (existingItem != undefined) {
    existingItem.cost += item.cost;
    existingItem.orders += item.orders;
  } else {
    newArr.push(item);
  }
});

console.log(newArr);

user_140143220 

let arr = [
  { id: 'ae0123', cost: 100.00, orders: 5 },
  { id: 'ae0123', cost: 50.00, orders: 5 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
]

let obj={};

arr.forEach(item=>{
  if(obj[item.id]){
    obj[item.id].cost +=item.cost;
    obj[item.id].orders +=item.orders;
  }
  else{
    obj[item.id]=item;
  }
});

const mappedArr=Object.keys(obj).map(key=>obj[key]);

console.log(mappedArr)

Try this

user_47561080

I'd go with reduce method of Array object, the above mentioned solution of using literal object works as well, but I think for such case, reduce makes code more readable and elegant:

const arr = [
  { id: 'ae0123', cost: 100.00, orders: 5 },
  { id: 'ae0123', cost: 50.00, orders: 5 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
];

const newArr = arr.reduce((acc, obj) => {
  if (!acc[obj.id]) {
    acc[obj.id] = obj;
  } else {
    acc[obj.id].cost += obj.cost;
    acc[obj.id].orders += obj.orders;
  }
  
  return acc;
}, {});

console.log( Object.values(newArr) );
user_32794260

Probably this is what you want

let arr = [
  { id: 'ae0123', cost: 100.00, orders: 5 },
  { id: 'ae0123', cost: 50.00, orders: 5 },
  { id: 'ae4321', cost: 75.00, orders: 1 }
]

let uniq = []
arr.map(x => {
  if(!uniq.includes(x.id)) uniq = [...uniq, x.id]
})

uniq = uniq.map(x => {
  let filtered = arr.filter(y => y.id === x)
  let res = filtered.shift()
  for(const z of filtered) {
    const {cost, orders} = z
    res.cost += cost
    res.orders += orders
  }
  return res
})

console.log(uniq)

user_118745540 
let newArr = []

arr.forEach((el, ind) => { 
    let uniqueId = el.id;
    let obj = el;
    let multiple = false;
    arr.forEach((e, i) => {
        if(e.id == uniqueId && ind != i ) {
            el.cost += e.cost;
            el.orders += e.orders;
             multiple = true;
             arr.splice(i,1);
             newArr.push(el)
        }
    });

    if(!multiple){
        newArr.push(obj);
    }

});

Tell me if it works, this will create a new array with the objects.

user_140389070
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