I have an array of objects(shopping cart) and I want to remove duplicates that have same obj.id and obj.arr an empty array.After that to increase obj.quantity by one. Here is the original arr:

const cart = [
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 1
    },
    {
        "id": 2,
        "name": "pen",
        "arr": ["asa", "asd"],
        "quantity": 3
    },
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 1
    },
    {
        "id": 3,
        "name": "ball pen",
        "arr": ["azx", "dcv"],
        "quantity": 1
    }
]

Expected output should be like this:

const cart = [
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 2
    },
    {
        "id": 2,
        "name": "pen",
        "arr": ["asa", "asd"],
        "quantity": 3
    },
    {
        "id": 3,
        "name": "ball pen",
        "arr": ["azx", "dcv"],
        "quantity": 1
    }
]

I don't know how to update object.quantity after removing the duplicate. And if possible I want to keep the item with smallest index.
Could you please help me?
Thank you

CodePudding user response：

To keep the order I would

• build up a map with the id as key and an array with the objects as value
• iterate this map and check for duplicates (= more than one object in array)
• check for the empty array field on all duplicates
• increase quantity on first occuring and overwrite existing entry (assuming all duplicates have the same quantity and it should only be increased by one, even if there are more than two duplicates)
• rebuild cart

const cart = [{
  "id": 1,
  "name": "book",
  "arr": [],
  "quantity": 1
}, {
  "id": 2,
  "name": "pen",
  "arr": ["asa", "asd"],
  "quantity": 3
}, {
  "id": 1,
  "name": "book",
  "arr": [],
  "quantity": 1
}, {
  "id": 3,
  "name": "ball pen",
  "arr": ["azx", "dcv"],
  "quantity": 1
}]

function removeDuplicates(cart) {
  
  let map = new Map()

  // groupBy id
  cart.forEach(obj => {
    let entry = map.has(obj.id)
    if (entry) {
      let value = map.get(obj.id)
      map.set(obj.id, [...value, obj])
    } else {
      map.set(obj.id, [obj])
    }
  })


  map.forEach((value, key) => {

    // doubles?
    if (value.length > 1) {

      let allEmptyArrays = value.every(obj => obj.arr.length === 0)

      if (allEmptyArrays) {
        // keep only the first value
        let keepValue = value[0]
        // adjust quantity
        keepValue.quantity  
        // overwrite existing entry
        map.set(key, [keepValue])
      }
    }
  })

  // rebuild cart
  return Array.from(map).map(([_, value]) => value[0])
}

console.log(removeDuplicates(cart))

CodePudding user response：

Modified code from How to remove all duplicates from an array of objects?. instead of filter I used reduce to then find and update the quantity of the duplicated item

const cart = [
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 1
    },
    {
        "id": 2,
        "name": "pen",
        "arr": ["asa", "asd"],
        "quantity": 3
    },
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 1
    },
    {
        "id": 3,
        "name": "ball pen",
        "arr": ["azx", "dcv"],
        "quantity": 1
    }
]

function findDupUpdateQty(arr){
return arr.reduce((acc, currentVal, index, self) => {
   if(index === self.findIndex((e)=> e.id === currentVal.id && e.arr.length === currentVal.arr.length)){
     acc.push(currentVal)
   } else {
   //if there's a duplicate then update quanitity
    acc[acc.findIndex((e)=> e.id === currentVal.id && e.arr.length === currentVal.arr.length)].quantity  = currentVal.quantity
   }
   return acc
},[])
}

console.log(findDupUpdateQty(cart))

Edits with some of @Corrl suggestions:

const cart = [
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 1
    },
    {
        "id": 2,
        "name": "pen",
        "arr": ["asa", "asd"],
        "quantity": 3
    },
    {
        "id": 1,
        "name": "book",
        "arr": [],
        "quantity": 1
    },
    {
        "id": 3,
        "name": "ball pen",
        "arr": ["azx", "dcv"],
        "quantity": 1
    }
]

function findDupUpdateQty(arr){
return arr.reduce((acc, currentVal, index, self) => {                     //check if both arrays are the same
   let firstFoundIndex = self.findIndex((e)=> e.id === currentVal.id && JSON.stringify(e.arr) === JSON.stringify(currentVal.arr))
   if(index === firstFoundIndex){
     acc.push(currentVal)
   } else {
    self[firstFoundIndex].quantity  = currentVal.quantity
   }
   return acc
},[])
}

console.log(findDupUpdateQty(cart))