How to find index deep in javascript array and return other part of array?

Question

I want to return rj: Object below, and I have an index key to match, kid: 1. What's the best/fastest way of doing considerg the main Object can contain > 10k items?

Object
 coord: MM.Coordinate
 data: Object
 geometry: Object
 properties: Object
   kid: 1            <== index id
   rj: Object        <== object i want
   __proto__: Object
__proto__: Object
element: HTMLDivElement
location: MM.Location
touch: true
__proto__: Object

How does this main object look like? Is this object the main? or is this just an entry of the main object? — Joseph
– Joseph, Commented Jan 14, 2013 at 22:46
Ah, sorry, it's from Chrome console. Top Object is main, yes. So I'll have 10k's of those. Then the unique identifier is deep in Object[properties[kid]], and the object I actually want is its next door neighbour. — knutole
– knutole, Commented Jan 14, 2013 at 22:48
Is the main object sorted somehow? Do you need to find more than one item by its unique id? — Bergi
– Bergi, Commented Jan 14, 2013 at 22:48
@Bergi I need to find many of these, so performance is an issue. But there's no index - unless kid counts as index. I mean, that would be great! ;) — knutole
– knutole, Commented Jan 14, 2013 at 22:49
the main object is an array? how does the collection look like from main? Also, is it assured that all entries have properties,kid and rj properties? — Joseph
– Joseph, Commented Jan 14, 2013 at 22:50

Bergi · Accepted Answer · 2013-01-14 22:53:28Z

1

If you need to find many objects, you can build a lookup table. Iterate over your collection of main objects, and store them in an key-value-map (simple object) by their identifier:

var mainsByKid = {}; // if the keys are integers (and not sparse), use an array
for (var i=0; i<mains.length; i++) {
     var main = mains[i],
         key = main.properties.kid; // must be unique
     mainsByKid[key] = main;
}

Now you can simply access your object by

mainsByKid[1];

answered Jan 14, 2013 at 22:53

Bergi

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3 Comments

Joseph Over a year ago

a for-in loop should be used on objects, unless the object in question is an array.

Bergi Over a year ago

Until we don't know how the collection really looks, I can only assume it is an array. Had upvoted your comments on the question already :-)

knutole Over a year ago

Thanks a lot, this is what I need. Turns out mapbox.js which I'm working with already had implement basically the exact same thing. Thanks again.

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