Get sum of duplicate obj in a nested array object

May 9, 2022

I have an obj array like this:

[
  {
    "feeTypeTitle": "STORAGE",
    "itemFees": [
      {
        "idx": 0,
        "itemTitle": "Apple iPhone 11 128GB",
        "itemFee": 4,
        "feeType": "STORAGE"
      },
      {
        "idx": 1,
        "itemTitle": "Sony FWD-40WD650/T",
        "itemFee": 4,
        "feeType": "STORAGE"
      },
      {
        "idx": 1,
        "itemTitle": "Sony FWD-40WD650/T",
        "itemFee": 2,
        "feeType": "STORAGE"
      }
    ]
  },
  {
    "feeTypeTitle": "VERIFICATION",
    "itemFees": [
      {
        "idx": 0,
        "itemTitle": "Apple iPhone 11 128GB",
        "itemFee": 5,
        "feeType": "VERIFICATION"
      },
      {
        "idx": 1,
        "itemTitle": "Sony FWD-40WD650/T",
        "itemFee": 5,
        "feeType": "VERIFICATION"
      }
    ]
  }
]

You can see in STORAGE, there are 2 items that same title, idx number. I want to merge and sum the itemFee of these duplicates and return same array structure. The result I want is:

[
  {
    "feeTypeTitle": "STORAGE",
    "itemFees": [
      {
        "idx": 0,
        "itemTitle": "Apple iPhone 11 128GB",
        "itemFee": 4,
        "feeType": "STORAGE"
      },
      {
        "idx": 1,
        "itemTitle": "Sony FWD-40WD650/T",
        "itemFee": 6, // <- sum value
        "feeType": "STORAGE"
      }
    ]
  },
  {
    "feeTypeTitle": "VERIFICATION",
    "itemFees": [
      {
        "idx": 0,
        "itemTitle": "Apple iPhone 11 128GB",
        "itemFee": 5,
        "feeType": "VERIFICATION"
      },
      {
        "idx": 1,
        "itemTitle": "Sony FWD-40WD650/T",
        "itemFee": 5,
        "feeType": "VERIFICATION"
      }
    ]
  }
]

How do I do this with vanilla js, ES6?

Thank you for help

>Solution :

You can do:

const data = [{feeTypeTitle: 'STORAGE',itemFees: [{idx: 0,itemTitle: 'Apple iPhone 11 128GB',itemFee: 4,feeType: 'STORAGE',},{idx: 1,itemTitle: 'Sony FWD-40WD650/T',itemFee: 4,feeType: 'STORAGE',},{idx: 1,itemTitle: 'Sony FWD-40WD650/T',itemFee: 2,feeType: 'STORAGE',},],},{feeTypeTitle: 'VERIFICATION',itemFees: [{idx: 0,itemTitle: 'Apple iPhone 11 128GB',itemFee: 5,feeType: 'VERIFICATION',},{idx: 1,itemTitle: 'Sony FWD-40WD650/T',itemFee: 5,feeType: 'VERIFICATION',},],},]

const result = data.map((o) => {
  const itemFeesHash = o.itemFees.reduce((a, c) => {
    a[c.idx] = a[c.idx] || { ...c, itemFee: 0 }
    a[c.idx].itemFee += c.itemFee
    return a
  }, {})
  o.itemFees = Object.values(itemFeesHash)
  return o
})

console.log(result)