How to get list of unique objects from list in javascript

Question

I need a list of unique objects based on a specific key.

const array = [
  {"name": "Joe", "age": 42},
  {"name": "Donald", "age": 69},
  {"name": "John", "age": 42},
]

How can i get a list of unique objects selected from the list assuming i want a list of people with unique ages.

const result = [
  {"name": "Joe", "age": 42},
  {"name": "Donald", "age": 69}
]

How can this be done in a performant way, is there a better way than iterating through the elements in a foreach and adding it if it does not exist in the resulting array?

Does this answer your question? Filter array to unique objects by object.property - it's not an exact fit, but it may help — evolutionxbox
– evolutionxbox, Commented Mar 11, 2021 at 12:22

trincot · Accepted Answer · 2021-03-11 12:20:05Z

3

One way is to feed the array to a Map where you key them by age. That will eliminate duplicates, only retaining the last in the series of duplicates. Then extract the values again from it:

const array = [{"name": "Joe", "age": 42},{"name": "Donald", "age": 69},{"name": "John", "age": 42}];
const uniques = Array.from(new Map(array.map(o => [o.age, o])).values());
console.log(uniques);

If you want to retain the first of duplicates, then first reverse the array.

answered Mar 11, 2021 at 12:20

trincot

357k38 gold badges282 silver badges338 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

pilchard · Accepted Answer · 2021-03-11 15:17:18Z

0

Another option is to track seen values, here using a Set passed as a closure and checking for values using its .has() method to return a boolean to a filter() call. This will retain the first seen objects.

const array = [
  { "name": "Joe", "age": 42 },
  { "name": "Donald", "age": 69 },
  { "name": "John", "age": 42 },
]

const unique = (seen => array.filter(o => !seen.has(o.age) && seen.add(o.age)))(new Set());

console.log(unique)

answered Mar 11, 2021 at 15:17

pilchard

13.1k5 gold badges14 silver badges27 bronze badges

Collectives™ on Stack Overflow

How to get list of unique objects from list in javascript

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related