Check whether an object with property value 'x' exists in an array in Javascript

Question

I have a lot of objects that I'm trying to filter out duplicates from. When an object has a property, IMAGEURL which is present in another object, I want to ignore this object and move on.

I'm using nodeJS for this so if there's a library I can use to make it easier let me know.

I've done similar implementations before with checking string values in arrays, doing something like:

var arr = ['foo', 'bar'];
if(arr.indexOf('foo') == -1){
   arr.push('foo')
}

But this won't work for objects, as best I can tell. What are my options here? To put it more simply:

var obj1 = {IMAGEURL: 'http://whatever.com/1'};
var obj2 = {IMAGEURL: 'http://whatever.com/2'};
var obj3 = {IMAGEURL: 'http://whatever.com/1'};

var arr = [obj1, obj2, obj3];
var uniqueArr = [];

for (var i = 0; i<arr.length; i++){
    // For all the iterations of 'uniqueArr', if uniqueArr[interation].IMAGEURL == arr[i].IMAGEURL, don't add arr[i] to uniqueArr
}

How can I do this?

SheetJS · Accepted Answer · 2013-08-17 04:26:34Z

12

You can just use an inner loop (keeping track of whether we've seen the loop by using a seen variable -- you can actually use labels here, but I find the variable method to be easier to read):

for (var i = 0; i<arr.length; i++){
    var seen = false;
    for(var j = 0; j != uniqueArr.length; ++j) {
        if(uniqueArr[j].IMAGEURL == arr[i].IMAGEURL) seen = true;
    }
    if(!seen) uniqueArr.push(arr[i]);
}

answered Aug 17, 2013 at 4:26

SheetJS

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2 Comments

JVG Over a year ago

Can you explain why you've done j != uniqueArr.length and not j < uniqueArr.length? Don't quite see what's going on here.

SheetJS Over a year ago

@Jascination you can do < instead of != in this case. In this particular case, since j increases by 1 each step, both yield the same results. I just use != in these loops by default (opting for < or > when it is necessary)

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

Here is a concise way:

var uniqueArr = arr.filter(function(obj){
    if(obj.IMAGEURL in this) return false;
    return this[obj.IMAGEURL] = true;
}, {});

http://jsfiddle.net/rneTR/2

Note: this is concise, but orders of magnitude slower than Nirk's answer.

See also: http://monkeyandcrow.com/blog/why_javascripts_filter_is_slow/

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 17, 2013 at 4:46

bfavaretto

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1 Comment

SheetJS Over a year ago

You could do

uniqueArr = arr.filter(function(obj){return (uniqueArr.map(function(x){return x.IMAGEURL;}).indexOf(obj.IMAGEURL) != -1) ? false : (uniqueArr.push(obj), true);});

, but I strongly advise against it unless you know what you are doing

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Check whether an object with property value 'x' exists in an array in Javascript

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Note: this is concise, but orders of magnitude slower than Nirk's answer.

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Note: this is concise, but orders of magnitude slower than Nirk's answer.

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