Unique values in javascript hash

Question

I need to push a hash into array only if it doesn't contain the hash that i want to add. For example i have an array of hashes :

var someArray = [
        {field_1 : "someValue_1", field_2 : "someValue_2"},
        {field_1 : "someValue_3", field_2 : "someValue_4"},
        {field_1 : "someValue_5", field_2 : "someValue_6"}
    ]

The value

{field_1 : "someValue_1", field_2 : "someValue_2"}

should not be pushed into array as it is already there, but the value

{field_1 : "someValue_7", field_2 : "someValue_8"}

should, as the array does't contain such value.

Is there any way to do it using jQuery?

Now i'm just using $.each loop and check if the array contains some hash. If it does i trigger a flag. But i don't like this solution.

So you want to implement a composite unique index - I second Felix's what have you tried? You're going to have to do an array-search on each addition. Is the data in someArray sorted? (would simplify the search) — Rudu
– Rudu, Commented Jan 23, 2012 at 17:49
Now i'm just using $.each loop and check if the array contains some hash. If it does i trigger a flag. But i don't like this solution. — roman
– roman, Commented Jan 23, 2012 at 17:49
@Roman The other easy option is keeping a parallel hash with a composite key. — Dave Newton
– Dave Newton, Commented Jan 23, 2012 at 17:55

Umesh Patil · Accepted Answer · 2012-01-23 18:16:25Z

2

create custom prototype to check the presence of object in the array. Please check the prototype design below.

Array.prototype.contains=function(x){
 for(i in this){
   if((x.field_1==this[i].field_1)&&(x.field_2==this[i].field_2))
     return true;  
 }
 return false;
}

Using above prototype, you can check if object present in an array.

 var someArray = [
        {field_1 : "someValue_1", field_2 : "someValue_2"},
        {field_1 : "someValue_3", field_2 : "someValue_4"},
        {field_1 : "someValue_5", field_2 : "someValue_6"}
    ];

var a1={field_1 : "someValue_1", field_2 : "someValue_2"};
var a2={field_1 : "someValue_7", field_2 : "someValue_8"};

if(!someArray.contains(a1))   someArray.push(obj);  // it will NOT BE pushed
if(!someArray.contains(a2))   someArray.push(obj); // it will be pushed

answered Jan 23, 2012 at 18:16

Umesh Patil

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3 Comments

Kumsal Obuz Over a year ago

Could you reformat your code blocks?, Seeing you edited it with code blocks, thank you :)

Umesh Patil Over a year ago

Checking the existence before pushing into an array vs. Adding object into an array, if it doesn't contain the object. Both serves the same purpose :)

Kumsal Obuz Over a year ago

+1 I agree, my post just came after yours. As I was hitting the submit, I saw the "new answer" notification.

Kumsal Obuz · Accepted Answer · 2012-01-23 18:17:14Z

1

Alternatively, you can augment Array or define your prototype as the following :

Array.prototype.add = function(element){
    var itemExists = false;
    for(var i=0;i<this.length;i++){
        if(this[i]==element){
            itemExists = true;
            break;
        }
    }
    if(itemExists==false)
        return this.push(element);
}

So, using [].add(yourElement) will only add that element to your array if it doesn't already exist. Feel free to change the structure of the argument and if condition according to your needs.

answered Jan 23, 2012 at 18:17

Kumsal Obuz

8255 silver badges14 bronze badges

Comments

gotqn · Accepted Answer · 2012-01-23 18:11:41Z

I have faced this issue a lot of times, and what I always do is to write a function that returns true if the element is already in given set of elements.

function IsElementInSet(Element,Set)
{
    var ElementIsInSet=false;

    for(var i=0;i<Set.length;i++)
    {
        if(Set.field_1==Element.field_1&&Set.field_2==Element.field_2)
        {
                ElementIsInSet=true;
                break;
        }
    }

    return ElementIsInSet;
}

This is how I do the things. Create function that do some checks and give me true if the element is already there.

There are other possible solutions to optimise the search if you are working with big arrays and feel the things working slow, but I doubt you will.

EDIT: Also, about using parallel structure for saving current values - you can find it very tricky to have ordinary array (one dimension) in which only one value is saved - in your case it will be Element.field_1+Element.field_2 (concatenate the strings). Then you can write other function that check if there is given value in this array. I think the two solution are the same and it is question about style, not speed.

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