Javascript : set respected index variable value to true if array has duplicate values

Question

I have an array of object which might include duplicate values.

I want those array index variable value to true if those indexes has duplicate values.

Let say I have below array of objects

let arr = [
    {
        name :'abc',
        age : 20,
    },

    {
        name :'xyz',
        age : 25,
    },

    {
        name :'pqr',
        age : 22,
    },

    {
        name :'abc',
        age : 27,
    },

    {
        name :'abc',
        age : 26,
    },
]

so there is 3rd and 4th index which has duplicate name as 0th index. I want to set isError variable to true for 3rd and 4th index and for others I would like to set to false.

Any help would be great.

Thank you.

Ori Drori · Accepted Answer · 2019-04-18 12:04:36Z

1

Use a Set to store existing names, and map the array. Check in the Set, if a name exists, and assign to the isError variable. Add the current name to the Set. Create a new object with the original content, and isError:

const markDuplicates = arr => {
  const existingIds = new Set();
  
  return arr.map(o => {
    const isError = existingIds.has(o.name)
    
    existingIds.add(o.name)
    
    return { ...o, isError };
  })
}

const arr = [{"name":"abc","age":20},{"name":"xyz","age":25},{"name":"pqr","age":22},{"name":"abc","age":27},{"name":"abc","age":26}]

const result = markDuplicates(arr)

console.log(result)

answered Apr 18, 2019 at 12:04

Ori Drori

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Comments

brk · Accepted Answer · 2019-04-18 12:07:41Z

You can first sort the array & then use map. After sorting all the objects will be sorted in ascending order of name. Then use map which will return a new array and while returning check if the name in current object is same with previous object. If so then add a duplicate key and assign a value to it

 if (index !== 0 && item.name == k[index - 1].name) {

This line is omitting the check for first object in sorted array, because there is nothing to copy with previous object and item.name == k[index - 1].name is checking if the name is same with previous object

let arr = [{
    name: 'abc',
    age: 20,
  },

  {
    name: 'xyz',
    age: 25,
  },

  {
    name: 'pqr',
    age: 22,
  },

  {
    name: 'abc',
    age: 27,
  },

  {
    name: 'abc',
    age: 26,
  },
];
let k = arr.sort(function(a, b) {
  return a.name.localeCompare(b.name);
});
let z = k.map(function(item, index) {
  if (index !== 0 && item.name == k[index - 1].name) {
    return {
      name: item.name,
      age: item.age,
      duplicate: true
    }
  } else {
    return {
      name: item.name,
      age: item.age
    }
  }
});
console.log(z)

Code Maniac · Accepted Answer · 2019-04-18 12:13:29Z

0

You can use a object as tracker, add a key by name,

Loop through data if the name is already available on op as key then change current element isError property to true else create a new key on op and set current element isError to false

let arr = [{name :'abc',age : 20,},{name :'xyz',age : 25,},{name :'pqr',age : 22,},{name :'abc',age : 27,},{name :'abc',age : 26,},]

let op = {}

arr.forEach( (inp,index) => {
  if( op[inp.name] ){
    inp.isError = true
  } else{
    inp.isError = false
    op[inp.name] = inp
  }
})

console.log(arr)

edited Apr 18, 2019 at 12:13

answered Apr 18, 2019 at 12:04

Code Maniac

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