How unique an array of object with js by properties

Today, I will explain how to unique an array of object by property

Unique by a Single Property

If you want the objects in the array to be unique based on one property (e.g., id):

                                        
                                            const array = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
  { id: 1, name: 'Alice' }, // Duplicate based on id
];

const uniqueArray = Array.from(
  new Map(array.map(item => [item.id, item])).values()
);

console.log(uniqueArray);
// Output: [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }]

Unique by Multiple Properties

If you want uniqueness based on a combination of properties, you can create a unique key by combining the values of those properties:

                                        
                                            const array = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
  { id: 1, name: 'Alice' },
  { id: 1, name: 'Charlie' }, // Same id, different name
];

const uniqueArray = Array.from(
  new Map(array.map(item => [`${item.id}-${item.name}`, item])).values()
);

console.log(uniqueArray);
// Output: [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }, { id: 1, name: 'Charlie' }]

Using filter for Simplicity

Alternatively, you can use the filter method for uniqueness by checking if an item's index matches its first occurrence:

                                        
                                            const array = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
  { id: 1, name: 'Alice' },
];

const uniqueArray = array.filter(
  (item, index, self) =>
    index === self.findIndex(obj => obj.id === item.id)
);

console.log(uniqueArray);
// Output: [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }]

Explanation

  1. Map and Set: Efficient for large arrays because they use hashing for uniqueness.

  2. filter + findIndex: More readable but can be slower for large arrays due to nested iterations.

  3. Custom Combination Key: Use when uniqueness depends on multiple properties.

December 31st, 2024