Get JSON object by attribute

Question

Say I have this JSON object:

var images = {"success":"true", "images":[
     {"id":"1234","url":"asdf","tags":["cookie","chocolate"]},
     {"id":"5678","url":"qwer","tags":["pie","pumpkin"]}
]};

What would be the most efficient way to get the url of the image with an id of 5678? Can use jQuery.

How many do you have? If it's just a few (like less than 500), then it doesn't matter what approach you take. — beatgammit
– beatgammit, Commented Sep 17, 2011 at 3:18
There will probably be several hundred, but in some cases there could be a max of 1,000. — penguinrob
– penguinrob, Commented Sep 17, 2011 at 3:19
Could you show me any one of those approaches? It doesn't really matter how efficient it is, I just need something that gets the job done. — penguinrob
– penguinrob, Commented Sep 17, 2011 at 3:23

jfriend00 · Accepted Answer · 2011-09-17 03:24:14Z

12

Because it's an array and you're looking for an embedded property, not just a simple array value, there isn't really a super-efficient way to find it. There's the brute force mechanism of just walking through the array and compare each id to what you're looking for.

If you're going to be looking up these kinds of things in this same data structure multiple times and you want to speed it up, then you can convert the existing data structure into a different data structure that's more efficient for accessing by ID like this:

var imagesById = {
    "1234": {"url":"asdf","tags":["cookie","chocolate"]},
    "5678": {"url":"qwer","tags":["pie","pumpkin"]}
}

Then, finding an object by id is as simple as this:

imagesById["1234"]

answered Sep 17, 2011 at 3:24

jfriend00

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penguinrob Over a year ago

Ah, +1 for the putting into another data structure. I'll just do that once it first gets the JSON, to speed up further access.

user123444555621 · Accepted Answer · 2011-09-17 09:22:32Z

6

url = $.grep(images.images, function(item) { return item.id === '5678' })[0].url;

answered Sep 17, 2011 at 9:22

user123444555621

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penguinrob Over a year ago

I haven't heard of the grep function before in jQuery! +1 for that!

Matt Ball · Accepted Answer · 2011-09-17 03:27:58Z

2

Unless the IDs are sorted, you can't do better than plain old iteration:

var images = {"success":"true", "images":[
     {"id":"1234","url":"asdf","tags":["cookie","chocolate"]},
     {"id":"5678","url":"qwer","tags":["pie","pumpkin"]}
]};

var inner = images.images,
    targetId = '5678',
    found = null;

for (var i=0; i<inner.length; i++) {
    if (inner[i][id] === targetId) {
        found = inner[i];
        // do stuff...
        break;
    }
}

answered Sep 17, 2011 at 3:27

Matt Ball

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Comments

Simeon G · Accepted Answer · 2011-09-17 03:31:54Z

2

You'd have to loop through the array:

$.each(images.images,function(i,img) {
   if(img.url == "5678") {
        //do whatever you want with this url
    }
}

answered Sep 17, 2011 at 3:31

Simeon G

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