check if duplicates exist in array object

Question

I want to reaturn true/false if there is some duplicates on object array.

arr = [
     { nr:10, name: 'aba' },
     { nr:11, name: 'cba' },
     { nr:10, name: 'aba' }
]

 arr2 = [
         { year:2020, city: 'Aaa' },
         { year:2010, city: 'Bbb' },
         { year:2020, city: 'Aaa' }
    ]

I found many solutions for one value but what if we want to check the whole object. Do I have to do foreach?

 const result: T[] = [];
    for (const item of array) {
        if (!result.includes(item)) {
            result.push(item);
        }
    }
    return result;

Does this answer your question? How can I check if the array of objects have duplicate property values? — Yong Shun
– Yong Shun, Commented Dec 12, 2022 at 13:19
@YongShun I tried to use the method from these answers to compare more than one value (year, city), but I don't know how to do it. — VMG
– VMG, Commented Dec 12, 2022 at 13:25

Matias Bertoni · Accepted Answer · 2022-12-12 13:41:00Z

1

you can use JSON.stringify and map and some array methods.

let arr = [
     { nr:10, name: 'aba' },
     { nr:11, name: 'cba' },
     { nr:10, name: 'aba' }

]


 let valuesStringify = arr2.map(x => JSON.stringify(x));

 let duplicate = valuesStringify.some((item, i) => valuesStringify.indexOf(item) !== i)

console.log(duplicate) //true

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edited Dec 12, 2022 at 13:41

answered Dec 12, 2022 at 13:35

Matias Bertoni

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Comments

Andrew Allen · Accepted Answer · 2022-12-12 13:51:06Z

Using combo of Array.prototype.some, Array.prototype.every and Object.entries

This checks each item of array against the rest of the array (slice(index + 1)) to see if some object is equal.

function hasDuplicates(arr) {
  // check each item of array against rest of the array
  return arr.some((obj, index) => arr.slice(index + 1).some(obj2 => {
    // check obj is equal obj2
    return Object.entries(obj).every(([key, value]) => obj2[key] === value)
  }))
}

let arr = [
  { nr:10, name: 'aba' },
  { nr:11, name: 'cba' },
  { nr:10, name: 'aba' }
];

let arr2 = [
  { year:2020, city: 'Aaa' },
  { year:2010, city: 'Bbb' },
  { year:2020, city: 'Ccc' }
];

console.log(hasDuplicates(arr)); // true
console.log(hasDuplicates(arr2)); // false

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