How can I check if an array contains another array?

Question

At first sight it's very simple, but I'm having some problems to do this without using a lot of nested loops.

Example:

var father:Array = new Array(0,1,2,3,4,5);
var son:Array = new Array(3,4,5);

father.contains(son) // returns true or 4(the starting index if the contained array)

Peter Hall · Accepted Answer · 2012-07-26 23:58:53Z

5

ActionScript 3 actually supports some slightly crazy stuff, due to the fact that, in the early days, Adobe/Macromedia were trying to make it compliant with Ecmascript.

So... you can do this:

var a1:Array = [1,2,3,4,5,6,7,8,9];
var a2:Array = [3,4,5];

// borrow String's indexOf function, and it magically works on Arrays
// but rename it because Array already has a different indexOf function
a1.indexOf2 = String.prototype.indexOf;

trace(a1.indexOf2(a2) > -1); // true

But you need to be a little bit careful because it will convert all the elements to Strings for the equality test. For primitives, it mostly won't matter but it will break badly with objects as they'll all be converted to "[object Object]" or to whatever their toString() returns.

Also, if you wanted to use the actual index for anything, rather than just checking it's not -1, you have to divide by two, as the number is double what you'd expect. I don't exactly know why this is :)

If you need something more general and reliable, you'd be better off writing a function to do an explicit search. This is a quick example, which I just wrote so could easily be bug-ridden:

    public function find(haystack:Array, needle:Array):int 
    {
        var index:int = -1;
        while(index <= haystack.length - needle.length)
        {
            index++;
            index = haystack.indexOf(needle[0], index);
            for( var i:int = 1; i<needle.length; i++)
            {
                if(haystack[index+i] != needle[i])
                {
                    continue;
                }
            }
            if( i == needle.length)
            {
                return index;
            }
        }
        return -1;
    }

edited Jul 26, 2012 at 23:58

answered Jul 26, 2012 at 22:50

Peter Hall

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2 Comments

Marcelo Assis Over a year ago

Thanks, worked just like I needed! Just for curiosity, how do you discovered that?

Peter Hall Over a year ago

I have been using Flash since before it had Actionscript at all, so I've seen the language grow from nothing and all the little warts along the way :)

OMA · Accepted Answer · 2013-02-24 14:51:16Z

0

Try this for simplicity:

// Determines if an array contains en element (similar to the PHP function with the same name)
public function in_array(needle:*, haystack:Array):Boolean 
{
    for each (var element:* in haystack)
    {
        if (element == needle) {return true;}
    }
    return false;
}

answered Feb 24, 2013 at 14:51

OMA

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