Distinct objects in array according to certain value

Question

I'm wondering how to get an array of objects with distinct objects. I'm managing a database where we've modifications constantly and we want to get the lasts modifications on objects in order to display them. I'm using NeDB and we can't distinct values so I've got an array of objects which is sorted by date but I don't know how to get an array of objects with unique name.

Distinct objects means :

Imagine I've got 3 objects like

{name: "Toto", modif: "added", createdAt : "05/08/2017"}
{name: "Toto", modif: "updated", createdAt: "05/09/2017"}
{name: "Toto", modif: "deleted", createdAt: "05/10/2017"}

I want to only keep the first Toto here.

We don't care about that date because the array of objects is already sorted by date.

distinct object means same object reference or objects with same keys/values? — Nina Scholz
– Nina Scholz, Commented May 9, 2017 at 7:41
Yes, my mistake I didn't read myself and wanted to put 3 objects for no misunderstanding — Tewan
– Tewan, Commented May 9, 2017 at 8:06

Nina Scholz · Accepted Answer · 2017-05-09 08:25:00Z

3

You could use a hash table for keeping a flag for same named objects and filter the given array.

var objects = [{ name: "Toto", modif: "added", createdAt: "05/08/2017" }, { name: "Toto", modif: "updated", createdAt: "05/09/2017" }, { name: "Toto", modif: "deleted", createdAt: "05/10/2017" }],
    unique = objects.filter(function (hash) {
        return function (o) {
            if (!hash[o.name]) {
                hash[o.name] = true;
                return true;
            }
        };
    }(Object.create(null)));

console.log(unique);

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edited May 9, 2017 at 8:25

answered May 9, 2017 at 7:57

Nina Scholz

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3 Comments

user663031 Over a year ago

return hash[o.name] = true;?

Nina Scholz Over a year ago

@torazaburo, right, but it's one time bad and one time good to return and make an assignment at the same time. i don't know.

user663031 Over a year ago

Right up there with the trick of creating magic variables by misusing function parameters.

user663031 · Accepted Answer · 2017-05-09 09:52:44Z

0

Filter the array to include only those elements such that a search for the first element in the array with that name yields that element itself.

data.filter(elt => data.find(elt2 => elt.name === elt2.name) === elt)

answered May 9, 2017 at 9:52

user663031

1 Comment

magicgregz Over a year ago

this is O(n^2) though.

magicgregz · Accepted Answer · 2018-03-02 18:16:11Z

IMO the most efficient way to solve this is to reduce the array by the key you care about while keeping the first value set for the key.

var uniqueObjectsByKey = function(array, key){
  return Object.values(array.reduce(function(obj, value) { 
    obj[value[key]] = obj[value[key]] !==undefined ? obj[value[key]] : value; 
    return obj 
  }, {}))
}
    
var array = [
  {name: "Toto", modif: "added", createdAt : "05/08/2017"},
  {name: "Toto", modif: "updated", createdAt: "05/09/2017"},
  {name: "Toto", modif: "deleted", createdAt: "05/10/2017"}
]
    
uniqueObjectsByKey(array, 'Toto')

alternatively if you want an ES6 one line where YOUR_ARRAY is your array of objects and FILTER_KEY is the key on which you want unique objects:

Object.values(YOUR_ARRAY.reduce((obj, value) => ({[value[FILTER_KEY]]]: value[FILTER_KEY], ...obj }), {}))

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