How can I parse these javascript objects into a grouped 2d array?

Question

New to javascript so trying to wrap my head around working with different data structures.

Got a collection of objects such as:

{id:1234, photo:"pathtosomejpg"}
{id:1234, photo:"pathtosomejpg2"}
{id:1234, photo:"pathtosomejpg3"}
{id:2234, photo:"pathtosomejpg4"}
{id:2235, photo:"pathtosomejpg5"}

After I'm done looping I'd like to get a 2d array that has the id as the key, and the value is an array of all of the photo values that match that id.

Here's what I've tried:

var groupedImages = [];
var innerAlbumPhotos = [];

// foreach obj in collection
if groupedImages.hasOwnProperty(obj.id.toString())
 innerAlbumPhotos = groupedImages[obj.id.toString()];

innerAlbumPhotos.push(obj.photo);

groupedImages[obj.id.toString()] = innerAlbumPhotos;

How can I create the data structure described here?

Answer 1

Try the following:

var results = [];
arr.forEach(function( v ) {
  var target = results[ v.id ];
  target 
    ? target.push( v.photo ) 
    : ( results[ v.id ] = [ v.photo ] );
});

Demo: http://jsfiddle.net/elclanrs/YGNZE/4/

Answer 2

I would use a loop for each element of the array. If the id doesn't exist I create a new array for it and if the id exist I add the photo to it.

var data = [{id:1234, photo:"pathtosomejpg"},
    {id:1234, photo:"pathtosomejpg2"},
    {id:1234, photo:"pathtosomejpg3"},
    {id:2234, photo:"pathtosomejpg4"},
    {id:2235, photo:"pathtosomejpg5"}];

var result = [];
for (var i = 0; i < data.length; i++) {
    if (result[data[i].id]) {
        result[data[i].id].push(data[i].photo);
    } else {
        result[data[i].id] = [data[i].photo];
    }
}

Answer 3

Arrays in javascript has no keys, so if you set arr[1000] = 1, the array will have 1000 elements. So you should use an object instead.

var photo_index = {};
function indexPhoto( photo_object ){
  if( !photo_index[photo_object.id] )
    photo_index[photo_object.id] = [];
  photo_index[ photo_object.id ].push( photo_object.photo );
}

Then, call indexPhoto for all your object formatted like you described.