javascript Set with objects

Question

When merging array of strings, I can use Set and ES6 to remove duplicates like so:

const a = ["hello", "hi", "yo"]
const b = ["alo", "hi"]
const remove_hi = [
  ...new Set([
    ...a,
    ...b,
  ]),
]

But how do I compare and remove objects? Say I have this:

const a = [
  {id: "asd", name: "Hi"},
  {id: "fgh", name: "Hello"},
  {id: "123", name: "Hi"}
]
const b = [
  {id: "jkl", name: "Yo"},
  {id: "123", name: "Hi"}
]
// This will not work. It will have a duplicate of {id: "123", name: "Hi"}
const remove_hi = [
  ...new Set([
    ...a,
    ...b,
  ]),
]

How do I remove {id: "123", name: "Hi"} from a combined array with Set?

Possibly if the position of the objects keys would not change, but there must be a better more elegant way — Ben
– Ben, Commented Feb 12, 2021 at 22:55
Other ways will require iterating through each item in the Set and checking each object's properties and values. Possible, but extremely cumbersome. If I were in this situation, I'd take a step back and consider if there was a different way to approach the problem other than putting objects into a Set — CertainPerformance
– CertainPerformance, Commented Feb 12, 2021 at 22:56
Do you want to deduplicate by id, or by the combination of id and name? — Patrick Roberts
– Patrick Roberts, Commented Feb 12, 2021 at 22:57
Since you want to deduplicate by name, do you want to keep the fist occurrence or the last occurrence (say the first object had a different id than the second one with the same name, which one should be kept)? — Nick Parsons
– Nick Parsons, Commented Feb 12, 2021 at 23:06

Patrick Roberts · Accepted Answer · 2021-02-12 23:15:21Z

3

Use a Map to deduplicate by the key name:

const uniqueBy = (array, key) => [
  ...new Map(
    array.map(o => [key(o), o])
  ).values()
];

const a = [
  {id: "asd", name: "Hi"},
  {id: "fgh", name: "Hello"},
  {id: "123", name: "Hi"}
]
const b = [
  {id: "jkl", name: "Yo"},
  {id: "123", name: "Hi"}
]
const remove_hi = uniqueBy([...a, ...b], o => o.name);

console.log(remove_hi);

Note that deduplicating only by name will remove both {id: "asd", name: "Hi"} and {id: "123", name: "Hi"} since they'd be considered duplicates of the last {id: "123", name: "Hi"} in the array when keying by name.

Replace o.name with whatever key you want to deduplicate by.

edited Feb 12, 2021 at 23:15

answered Feb 12, 2021 at 23:04

Patrick Roberts

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