Data structure to store unique values in javascript

Question

What is the best data type to store unique values only? an array can have duplicates

[one, one, two]

and an object (? maybe wrong terminology) have unnecessary values for my current case

{one: something, two: something, three: something}

Shortly, I need something like this:

{one, two, three}

I am not sure what it is called, or if it does exist in js. Needing some enlightment.

Have you looked into sets? new Set(["one", "two", "three"]) — homam
– homam, Commented Nov 9, 2014 at 21:07
@homam Set is pretty cool and is exactly what OP might want. But it's ECMAScript 5 proposal. But soon it will be really awesome thing! — dfsq
– dfsq, Commented Nov 9, 2014 at 21:12
@homam I wasn't aware of sets! I will check them! thank you. — Mia
– Mia, Commented Nov 9, 2014 at 21:14
Similar questions: stackoverflow.com/questions/7958292/… stackoverflow.com/questions/5657219/… stackoverflow.com/questions/2523436/… — Stuart
– Stuart, Commented Nov 9, 2014 at 21:16

Kuba Jagoda · Accepted Answer · 2014-11-09 20:46:54Z

5

You mean a structure called Set, and in the current version of ECMAScript there's no such structure. It will be standarized in the next version, however it's available now in some browsers.

You can emulate set using object, but as you said that also involves unnecessary values. If you don't want to care about them, you can use a library that emulates Set, like http://collectionsjs.com/

answered Nov 9, 2014 at 20:46

Kuba Jagoda

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2 Comments

dfsq Over a year ago

Here is a Set at MDN. Support is actually pretty good already, major browsers, IE11+.

Kuba Jagoda Over a year ago

@dfsq Yet I still wouldn't recommend using it on production. Especially that Chrome supports it only after the user turns on a proper flag.

adeneo · Accepted Answer · 2014-11-09 20:51:14Z

4

The most common way to solve this is to use an array, and just check if it already has the value you want to insert, that way it contains only unique values.

if ( arr.indexOf(value) == -1 ) arr.push(value);

answered Nov 9, 2014 at 20:51

adeneo

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2 Comments

Mia Over a year ago

is it better to use {} or [] in this case? (processor and memory wise)

adeneo Over a year ago

Doesn't matter, but if you don't need keys and values, there's no good reason to use an object.

dfsq · Accepted Answer · 2014-11-09 21:05:02Z

In addition to obvious ways you can always create you own data structure on top of array if you need some more advanced functionality. For example:

function UArray(val) {
    this._values = [];
    if (typeof val !== 'undefined') {
        this.set(val);
    }
}
UArray.prototype.set = function(values) {
    this._values = this._values.concat(values).filter(function(el, i, arr) {
        return arr.indexOf(el) === i;
    });
};
UArray.prototype.get = function() {
    return this._values;
}

var uarr = new UArray();
uarr.set(['one', 'one', 'two']);

alert( uarr.get() );

uarr.set('two');
uarr.set(['three', 'one']);

alert( uarr.get() );

Such a custom data structure could be extended with additional necessary methods, i.e.:

remove to remove specific item
find to find item's index or -1 if not found,
etc.

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