Reduce and sum array of objects (JS)

Question

My data:

arr: [],
models: [
    { id: 1, name: "samsung", seller_id: 1, count: 56 },
    { id: 1, name: "samsung", seller_id: 2, count: 68 },
    { id: 2, name: "nokia", seller_id: 2, count: 45 },
    { id: 2, name: "nokia", seller_id: 3, count: 49 }
]

Expected Arr:

arr: [
    { id: 1, name: "samsung", count: 124 },
    { id: 2, name: "nokia", count: 94 }
]

It's my code to simplify models by removing repeated id:

this.models.forEach(mdl => {
    if (!this.arr.some(obj => obj.id === mdl.id)) {
        this.arr.push(mdl);
    }
});

But I can't sum counts.
How can I do that?

Also this: https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects — Mohammad Usman, Feb 06 '20 at 07:16

score 3 · Accepted Answer · answered Feb 06 '20 at 07:15

You can use Array.reduce():

var models = [
    { id: 1, name: "samsung", seller_id: 1, count: 56 },
    { id: 1, name: "samsung", seller_id: 2, count: 68 },
    { id: 2, name: "nokia", seller_id: 2, count: 45 },
    { id: 2, name: "nokia", seller_id: 3, count: 49 }
];

var arr = models.reduce((acc, item) => {
  let existItem = acc.find(({id}) => item.id === id);
  if(existItem) {
    existItem.count += item.count;
  } else {
    acc.push(item);
  }
  return acc;
}, []);

console.log(arr);

So, for your code, you can use this.arr and this.models replacing those variables from above which will look something like:

this.arr = this.models.reduce((acc, item) => {
  let existItem = acc.find(({id}) => item.id === id);
  if(existItem) {
    existItem.count += item.count;
  } else {
    acc.push(item);
  }
  return acc;
}, []);

score 0 · Answer 2 · answered Feb 06 '20 at 07:18

You can use Object.values instead of some. Inside the reduce callback create an object with key as id and value from the models. Then use Object.values to create an array of the values

let models = [{
    id: 1,
    name: "samsung",
    seller_id: 1,
    count: 56
  },
  {
    id: 1,
    name: "samsung",
    seller_id: 2,
    count: 68
  },
  {
    id: 2,
    name: "nokia",
    seller_id: 2,
    count: 45
  },
  {
    id: 2,
    name: "nokia",
    seller_id: 3,
    count: 49
  }
]
let data = models.reduce((acc, curr) => {
  if (!acc[curr.id]) {
    acc[curr.id] = curr;
  } else {
    acc[curr.id].count += curr.count

  }
  return acc;
}, {})
console.log(Object.values(data))

Reduce and sum array of objects (JS)

2 Answers2