Angular2 avoid adding duplicate JSON objects to array

Question

I'm trying to avoid adding duplicate objects to an Angular2 array. For example let's say we have an array "Cars" and we put in a JSON object in that array that might be something like:

{
 "brand": "Acura"
 "engine": "2.4L"
 + others details
}

We can keep adding cars with to the array. My issue is now how to avoid adding the same car into the array again. If I were to add the same JSON as described above, it shouldn't be added. Would I have to iterate through all the existing objects in the array and compare each field of the JSON? This sounds like an expensive operation to me, or is there some more elegant/faster method?

Thanks!

Frank Modica · Accepted Answer · 2017-06-06 18:29:47Z

4

If each car has something unique about it (like an ID), you could use an object instead of an array:

var map = { };

function add(car) {
    if (map[car.id]) {
        return;
    }

    map[car.id] = car;
}

Your ID could be something else unique, like a combination of the brand and year or something similar.

map[car.brand + car.year] = car

answered Jun 6, 2017 at 18:29

Frank Modica

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jLee · Accepted Answer · 2017-06-06 18:33:29Z

0

You need to find or create a unique property on the items in the list, then you could use something like lodash to query the array by a property to see if that item already exists in the list before you add it.

Example from Lodash site

var users = [
  { 'user': 'barney',  'active': false },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': true }
];

// The `_.matches` iteratee shorthand.
_.findIndex(users, { 'user': 'fred', 'active': false });

answered Jun 6, 2017 at 18:33

jLee

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4 Comments

vgogov Over a year ago

Sweet thanks! I added an UUID to each JSON object and used the method: if ((_.findIndex(this.cars, {"id": car.id})) == -1) { this.cars.push(car) }

Frank Modica Over a year ago

Doesn't this solution still iterate through the collection?

developer033 Over a year ago

In addition to @FrankModica: Why did you suggest to use lodash while he could use exactly the same function natively? users.findIndex(user => user.id === <variable>). Or even the traditional indexOf...

jLee Over a year ago

@developer033 I suggested lodash because that is a library that I find myself using a lot for various common functions that prevent me from having to write my own. It just so happen that it was on my mind when I read his question and suggested it. Even though this one function does exist natively, I hope they find some of the other functions useful in the library.

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