How to build an associative array with jQuery/javascript?

Question

I have a large array in this format:

var cars = [{"brand":"Honda","year":"2002"},{"brand":"Toyota","year":"2000"},{"brand":"Subaru","year":"2009"}];

The array is very large (I made it small for demo purpose) and I want to organize cars of the same brand into an array, so the brand name will be the key for each sub-array, like this:

carsByBrand[ honda[], toyota[], subaru[] ]

I expected it would be straight forward but it's not so. I've tried several variations of the following code, but everytime it returns:

carsByBrand[item.brand] is undefined

 var carsByBrand = [];

   $.each(cars, function(i,item){
     carsByBrand[item.brand].push(item);
    });

    //console.debug(carsByBrand); //uncomment and look at this if you have Firebug

    alert(carsByBrand.length);

I've also tried carsByBrand[item['brand']], why doesn't this work, and how to do it?

jsBin: http://jsbin.com/orafos

Thilo · Accepted Answer · 2011-12-14 03:39:26Z

3

carsByBrand[item.brand].push(item);

That will only work if the array for that brand already exists, which it does not unless you initialize it first with an empty array.

Try

   brand = carsByBrand[item.brand];
   if (brand) {
       brand.push(item);
   else {    
       carsByBrand[item.brand] = [item];
   }

edited Dec 14, 2011 at 3:39

answered Dec 14, 2011 at 3:23

Thilo

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