How can I get the number of elements in a sparse array in Actionscript?

Question

Actionscript uses sparse arrays, so I can have an array like this:

var myArray:Array = new Array();
myArray[0] = "foo";
myArray[22] = "bar";

Now myArray.length will give me 23. Is there a way to get the actual number of items in the array without iterating every element?

Answer 1

If you don't want to iterate through the array, you can filter it:

var myArray:Array = new Array();
myArray[0] = "foo";
myArray[22] = "bar";

var numberOfItems:int = myArray.toString().split(',').filter(isItem).length;

function isItem(item:*, index:int, array:Array):Boolean
{
  return item != "";
}

Answer 2

By using for syntax, which will iterate the definded indexes:

public static function definedCount(arr:Array):uint {
    var ctr:uint = 0;
    for(ix:* in arr)
        ctr++;
    return ctr;
}

If you need to frequently check the count of items in a sparse array, you should wrap it an a collection class that independently keeps track of the count of items. Something like:

public class IndexedCollection { 
    private var _arr:Array = [];
    private var _itemCount:uint = 0;

    public function get count():uint {
        return _itemCount;
    }

    public function getItem(index:uint):* { 
        return _arr[index]; 
    }

    public function setItem(index:uint, value:*):void {
        if(_arr[index] === undefined)
            _itemCount++;
        _arr[index] = value; 
    }

    public function delete(index:uint):void { 
        if(_arr[index] === undefined) 
            return;
        delete _arr[index]; 
        _itemCount--;
    }
}

Answer 3

Fastest method should be to always use the inbuilt functions.

    function myFilter(item:*, index:int, array:Array):Boolean{
        if(item)
        {
            return true;
        }else{
            return false;
        }
    }

    var myArray:Array = new Array();
    myArray[0] = "foo";
    myArray[22] = "bar";
    trace(myArray.length) // 23
    var myMyNewArray:Array = myArray.filter(myFilter)
    trace(myMyNewArray .length) // 2