iterating array of objects and the key values in JS

Question

I have an array of objects

var j = [{"v1":["1","2","3"]}, {"v2":["4","5","6"]}, {"v3":["7","8","9"]}];

I want to check against the object property and perform some sort of logic. I am new to JS so I'm not sure of all the methods I have access to. Basically I want to compare the key value of the object to a string. If the key and the string are the same, then I would remove that object from the array. I'm not sure how to iterate through the object's key in the array.

var str = "v1";
for (var i in j) {
  if (i.key == str) {     // not sure how to access key value
    j.splice(i,1);
  }
}

Look into for loops (for the array) and for in (for the objects). — gpojd
– gpojd, Commented Oct 24, 2014 at 20:01
You should never iterate an array with for (var i in j) because that iterates all enumerable properties of the array, not just array elements. You can use either for (var i = 0; i < j.length; i++) or you can use j.forEach(function(val, index) {...}). The construct for (var i in j) is used to iterate all properties of an object. — jfriend00
– jfriend00, Commented Oct 24, 2014 at 20:01
Whenever I see this sort of data structure, I always wonder if the data structure is just wrong and it should be: var j = {"v1":["1","2","3"], "v2":["4","5","6"], "v3":["7","8","9"]}; so you can iterate the properties of j directly and skip the array entirely. If the properties are all meant to be unique and not in any particular order, this is a better way to structure the data. — jfriend00
– jfriend00, Commented Oct 24, 2014 at 20:04
@jfriend00 I'm new to JS so I am a bit confused on how ot construct my data at the moment. Thanks for bringing this up! I'll consider your suggestion — Liondancer
– Liondancer, Commented Oct 24, 2014 at 20:06
There's little benefit to having an array of objects of arrays where each object has a single key that increments. You should just have an array of arrays, and grab the index you want or iterate all of them. var j = [["1","2","3"], ["4","5","6"], ["7","8","9"]]; — user1106925
– user1106925, Commented Oct 24, 2014 at 20:07

Royi Namir · Accepted Answer · 2014-10-24 20:15:07Z

2

Try this :

var  j = [{"v1":["1","2","3"]}, {"v2":["4","5","6"]}, {"v3":["7","8","9"]}];

for (var i = 0; i < j.length; i++)
{
    for (var k in j[i]) //do use this if you need to iterate
    {
        if (k === "mySomething")
        {
            //...do your stuff
        }

    }
}

Edit

less verbose :

 for (var i = 0; i < j.length; i++)
    {
            if ("mySomething" in j[i])
            {
                //...do your stuff
            }

    }

edited Oct 24, 2014 at 20:15

answered Oct 24, 2014 at 19:59

Royi Namir

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2 Comments

user1106925 Over a year ago

@Liondancer: Aside from restructuring your data, this solution is more verbose than needed. There's no point to the for-in loop. It should just be if (str in j[i]) { /* do something with j[i][str] */ }

Liondancer Over a year ago

@RoyiNamir You helped me with my problem and provided a solution. However jfriend00 pointing out something and also provided a solution. I wish I can give you both check marks but I can't. I'm sorry but jfriend00 gave me a very helpful tip and an solution

jfriend00 · Accepted Answer · 2014-10-24 20:23:27Z

1

As we've been discussing in comments, there is seldom a reason to use an array of objects that each only have one property (unless you're using the array to maintain a specific order), so I thought perhaps your problem might be easier if the data was structured like this:

var j = {"v1":["1","2","3"], "v2":["4","5","6"], "v3":["7","8","9"]};

And, you could then iterate it like this:

for (var key in j) {
    console.log("j[" + key + "] = ", j[key]);
}

Working demo: http://jsfiddle.net/jfriend00/qdgzso1g/

answered Oct 24, 2014 at 20:23

jfriend00

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1 Comment

Liondancer Over a year ago

This helped a lot. Less iterations and simpler code. Thanks! =D

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