Delete certain properties from an object without a loop

Question

I'm trying to find the most efficient way of deleting properties from an object whose properties of commentCount and likeCount are both equal to 0. In the following example, Activity.3 would be removed. I don't want loop over them with a $.each() as that seems like it would take more time than necessary.

Activity = {
    0 : {
    'commentCount' : 10,
    'likeCount' : 20    
    },
    1 : {
    'commentCount' : 0,
    'likeCount' : 20    
    },
    2 : {
    'commentCount' : 10,
    'likeCount' : 0    
    },
    3 : {
    'commentCount' : 0,
    'likeCount' : 0    
    }
}

UPDATE

The circumstances of the creation of this object have come into question. To clarify, the Activity object can have up to 3 million properties inside of it. It's generated server side as an AJAX JSON response which is saved into memory. It includes more than just commentCount and likeCount that are used elsewhere, so I can't just not have the server not respond with things that have a 0 for both commentCount and likeCount.

Even if you found some syntax or framework that makes it seem like you aren't writing a loop, there is bound to be a loop going on under the covers. So, you might as well write the loop yourself so that you can make it as fast as possible. — lbstr
– lbstr, Commented Jun 19, 2012 at 18:49
I've provided an answer, but I have also come up with a stupid question: how does this object get populated? Couldn't you just prevent those properties from being added if their commentCount and likeCount sum to zero? — lbstr
– lbstr, Commented Jun 19, 2012 at 19:24
@lbstr That is a very good point, however, the data returned and stored via JSON has other properties that are used elsewhere. — user888750
– user888750, Commented Jun 19, 2012 at 21:02
@PatrickRobertSheaO'Connor OK, that's what I figured. Your edit definitely clears things up. My solution definitely isn't adequate since you are dealing with JSON that comes from the server. But, it begs the question, could you group your objects into buckets as my solution suggested? If the server-side code created JSON such that all activities with commentCount + likeCount == 0 were placed into a single bucket, you could just delete that bucket. Let me know if that is a possibility and I will update my answer. — lbstr
– lbstr, Commented Jun 19, 2012 at 21:44

Aaron Digulla · Accepted Answer · 2012-06-19 19:01:10Z

4

Ah, the smell of premature optimization ^_^

How many of these objects do you have? How many do you need to clean them? If the answers are "less than 1 million" and "once or rarely", it's probably not worth to bother.

If you need a quick and optimal way, here is an idea: Create a new data structure and setters for the properties. Every time they are set, check whether they are both 0 and put them into a "kill" list.

That way, you just have to iterate over the kill list.

[EDIT] With several million objects and the need for a quick cleanup, a kill list is the way to go, especially when the condition is rare (just a few objects match).

Just write a function that updates these properties and make sure all code goes through it to update them. Then, you can manage the kill list in there.

Or you can simply delete the object as soon as the function is called to set both or the second property to 0.

edited Jun 19, 2012 at 19:01

answered Jun 19, 2012 at 18:46

Aaron Digulla

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5 Comments

Ohgodwhy Over a year ago

Why bother with this? Even in a collection of 1 million elements using a new hashing algorithim all together will NARY be quicker than a simple loop. Splice is the best option here to jump into an array at any index and remove an element.

lbstr Over a year ago

well said. I also like the idea for performing this check inside of a setter. That way, you can forget about calling your "cleanse" function. +1

user888750 Over a year ago

There can be upwards of 3 million, and they need to be cleaned quite regularly. I've optimized it quite a bit already, I just wanted to get the opinion of the peanut gallery; however, it seems like it's full of down votes, is this reddit or something?? I'll take your suggestion and run with it. Thanks.

user888750 Over a year ago

Ohgodwhy, you can't use splice on an object.

Aaron Digulla Over a year ago

Depending on how often the setters are called, a kill list might really help. And you should edit your question and mention the numbers; otherwise your Q will sound a bit silly.

lbstr · Accepted Answer · 2012-06-19 23:06:06Z

I'm adding a second answer, because this solution comes from a completely different angle. In this solution, I attempt to find the fastest way to remove unwanted entries. I'm not aware of any way of doing this without loops, but I can think of several ways to do it with loops using jQuery as well as just raw javascript.

This jsperf shows all of the test cases side-by-side.

I'll explain each test and the caveats associated with each.

Raw JS: Slowest option. It looks like jQuery knows what they are doing with their $.each and $.map loops.

var obj;
for (var field in Activity) {
    if (Activity.hasOwnProperty(field)) {
        obj = Activity[field];
        if (obj.commentCount === 0 && obj.likeCount === 0) {
            delete Activity[field];
        }
    }
}

$.each: Tied for 2nd place. Cleaner syntax and faster than raw js loop above.

$.each(Activity, function(key, val){
    if (val.commentCount === 0 && val.likeCount === 0) {
        delete Activity[key];
    }
});

$.map (Object version): Tied for 2nd place. Caveat: only supported in jQuery >= 1.6.

Activity = $.map(Activity, function(val, key){
    if (val.commentCount === 0 && val.likeCount === 0) {
        return null;
    }
});

$.map (Array version): Fastest option. Caveat: You must use the $.makeArray function to convert your object to an array. I'm not sure if this is suitable for your needs.

var arrActivity = $.makeArray(Activity);
Activity = $.map(arrActivity, function(val, key){
    if (val.commentCount === 0 && val.likeCount === 0) {
        return null;
    }
});

Conclusion It looks like $.map is the fastest if you convert your object to an array using $.makeArray first.

lbstr · Accepted Answer · 2012-06-19 20:46:22Z

This is just a starting-point, but how about something like this? Basically, it puts the Activities into buckets based on the sum of their likeCount and commentCount. It makes it easy to kill all of the Activities with no likes or comments, but I would assume there is a trade-off. I'm not sure how you are inserting these things and reading them. So, you'll have to decide if this is worth it.

var ActivityMgr = function(){
    if(!(this instanceof ActivityMgr)){
        return new ActivityMgr();
    }

    this.activities = {};
};

ActivityMgr.prototype.add = function(activity){
    var bucket = parseInt(activity.commentCount, 10) + parseInt(activity.likeCount, 10);

    if (this.activities[bucket] === undefined) {
        this.activities[bucket] = [activity];
    }
    else {
        this.activities[bucket].push(activity);
    }

    this.cleanse();
};

ActivityMgr.prototype.cleanse = function(){
    this.activities[0] = [];
};

//Usage:
var activityMgr = new ActivityMgr();
activityMgr.add({
    likeCount: 0,
    commentCount: 10
});

EDIT: After posting this, it becomes incredibly apparent that if you are adding items in this manner, you could just not add them if they have no likes or comments. My guess is that things aren't that simple, so please provide some detail as to how things are added and updated.

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