ES6 array of hashes return unique array of hashes

Question

I have an object that looks like this:

const posts = [
               { id: 0, user: { id: 5564, name: 'john'} },
               { id: 1, user: { id: 5564, name: 'john'} },
               { id: 2, user: { id: 5560, name: 'jane'} }
              ]

I need an array of the unique user hashes like this:

[
 { id: 5564, name: 'john'},
 { id: 5560, name: 'jane'}
]

I'm able to retrieve all the users attributes from the posts array by doing:

const postUsers = posts.map(post => post.user)

which returns:

[
 { id: 5564, name: 'john'},
 { id: 5564, name: 'john'},
 { id: 5560, name: 'jane'}
]

where user john is listed twice

I've been able to get my desired result by doing:

const unique = {};
const uniqueUsers = [];
for(var i in postUsers){
  if(typeof(unique[postUsers[i].id]) == "undefined"){
    uniqueUsers.push(postUsers[i]);
  }
  unique[postUsers[i].id] = 0;
};
uniqueUsers

but there must be a cleaner way. I've also been able to return the unique ids of all users by doing:

var ids = posts.map(post => post.user.id)

var uniqueIds = Array.from(new Set(ids)).sort(); which returns [5564, 5560]

not sure if that helps. this article helped me a little https://medium.com/tomincode/removing-array-duplicates-in-es6-551721c7e53f

Is just the `id` sufficient to check for uniqueness or do you need to consider both `id` and `name`? — slider, Jul 01 '19 at 21:05
These are called *objects* in JavaScript, not hashes (that's the Perl term). — Barmar, Jul 01 '19 at 21:06
`Object.values(posts.reduce((r, {user}) => r[user.id] ? r : (r[user.id] = user, r), {}))` — pishpish, Jul 01 '19 at 21:07

score 0 · Answer 1 · answered Jul 01 '19 at 21:09

You could take a Map and get only the unique users.

const
    posts = [{ id: 0, user: { id: 5564, name: 'john'} }, { id: 1, user: { id: 5564, name: 'john'} }, { id: 2, user: { id: 5560, name: 'jane'} }],
    unique = Array.from(posts.reduce((m, { user }) => m.set(user.id, user), new Map).values());

console.log(unique);

score 0 · Answer 2 · answered Jul 01 '19 at 21:09

0

If you don't mind using lodash you can do something like

const users = _map.(posts, 'user') // To get the list of users
_.uniqBy(users, 'id') // to get the uniq ones

answered Jul 01 '19 at 21:09

Agustin Cornu

186
5

score 0 · Answer 3 · answered Jul 01 '19 at 21:10

Put the objects directly in uniqueUsers, then use Object.values() at the end to convert the object to an array.

const posts = [
   { id: 0, user: { id: 5564, name: 'john'} },
   { id: 1, user: { id: 5564, name: 'john'} },
   { id: 2, user: { id: 5560, name: 'jane'} }
];
let uniqueUsers = {};
posts.forEach(({user}) => uniqueUsers[user.id] = user);
uniqueUsers = Object.values(uniqueUsers);
console.log(uniqueUsers);

Get Off My Lawn · Answer 4 · 2019-07-01T21:17:53.557

Use reduce to reduce the array by checking if the value is already in the array. If it is already in the array, return the current state of the array, otherwise add the item to the array.

const posts = [
  { id: 0, user: { id: 5564, name: 'john'} },
  { id: 1, user: { id: 5564, name: 'john'} },
  { id: 2, user: { id: 5560, name: 'jane'} }
]

const r = posts.map(i => i.user).reduce((acc, itm) => {
  return !acc.find(i => i.id == itm.id) && acc.concat(itm) || acc
}, [])

console.log(r)

ES6 array of hashes return unique array of hashes

4 Answers4