Confused about javascript arrays using index and strings for multidimensional

Question

I have a situation where I wish to build an array that can be accessed via:

myArray['Foo'].push(myObj);

But I do not know how to create it from scratch. From what I had read I thought maybe the following would do it:

var myArray = new Array(new Array());

Problem is that it only lets me use integers to reference the myArray[]. If I ignore this limitation and try the following it errors saying it doesn't have .push():

myArray[i].push(myObj);

I presume this is because myArray[i] is returning a string?

So my question is, how do I build a dynamic array where I reference the first dimension using strings and can then push and pop on the second dimension? Also if I take this approach, can I use push and pop for adding the string to the first dimension?

I thought about this a bit more before and wrote some code I thought may work, which it does.

var myArray = new Object();

var myObj = new Object();
var myObj2 = new Object();
var myObj3 = new Object();

myObj.name = "Harry";
myObj2.name = "Curly";
myObj3.name = "Moe";

myArray["first"] = new Array()
myArray["first"].push(myObj);
myArray["first"].push(myObj2);
myArray["first"].push(myObj3);

myArray["second"] = new Array()
myArray["second"].push(myObj2);

myArray["third"] = new Array()
myArray["third"].push(myObj3);

iterate(myArray, "first");
iterate(myArray, "second");
iterate(myArray, "third");

function iterate(array, name) {
    for(i = 0, l = myArray[name].length; i < l; i++) {
        console.log(" " + name + ": " + i + " value " + myArray[name][i].name);
    }
}

Is the above the correct way to go about it?

I'm sure I've got some terminology problems with the above, let me know and I'll edit it so it's correct.

I don't think javascript has associative arrays. You have to use objects for that. What is happening is that it's adding an object property to the array. — PitaJ
– PitaJ, Commented Jan 19, 2013 at 5:19
Just realised the error I am getting is caused by length(), I'll fix my question. Hmm. I think I've answered my own question, though I'm still kinda confused by arrays. Should I answer myself? — Metalskin
– Metalskin, Commented Jan 19, 2013 at 5:29
@PitaJ What tends to confuse people is that Javascript allows objects to be accessed as if they were associative arrays. But that doesn't make numeric and associative arrays interchangeable, like they are in PHP. — Barmar
– Barmar, Commented Jan 19, 2013 at 5:52

Cory Kendall · Accepted Answer · 2013-01-19 05:59:48Z

3

What you are calling myArray is not an array, it is an Object. Either of the following are acceptable:

var myObject = {}
var myObject = new Object();

All of the following lines do the same thing; they create a key called "first" in the object "myObject" and store a new, empty array (into which you can push):

myObject['first'] = new Array();
myObject['first'] = [];
myObject.first = new Array();
myObject.first = [];

Now you can push into this array:

myArray["first"].push("hello");

Here's another way to write this from scratch:

var myObject = {
    first: ["hello"]
};

So perhaps now the answers to your questions become more clear:

How do I build a dynamic array where I reference the first dimension using strings and can then push and pop on the second dimension?

By making the "first", or outer dimension be an object rather than an array.

Also if I take this approach, can I use push and pop for adding the string to the first dimension?

Nope, but you can use

myObject.somewhereNew = [];

edited Jan 19, 2013 at 5:59

answered Jan 19, 2013 at 5:38

Cory Kendall

7,3349 gold badges40 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Metalskin Over a year ago

Thanks Cory, that explains it all very nicely.

Barmar Over a year ago

Your "from scratch" should be var myObject = {first: ["hello"]};, shouldn't it?

Collectives™ on Stack Overflow

Confused about javascript arrays using index and strings for multidimensional

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related