$str = 'aabbccaaaaddaaeeffbb';
while ($str =~ s/(.)(.*?)\1+/$1$2/g) {}
print $str;

OUTPUT:
abcdef

Based on the same concept, if you can’t transpose the array, you could just do a single loop through it and assign its values as keys and values to another array:
(reminder i don’t know AS, this code is based on what i’ve seen above, try to decipher the logic)

var firstArray:Array = thestring.split('');
var secondArray:Array = new Array();
firstArray.forEach(
    function (){
        secondArray[item] = item;
    }
);


Reorder the second array after the operation, since it’s shorter the reordering operation is more efficient.

There’s no guarantee that the whole thing will be faster, if you have the time to benchmark it, maybe it’s worth a shot. Off I go.

[...] In my previous article TLP has commented and created a better method. You can see his post here. [...]

Worked for me.

Anyway, I came up with this little gem that’s a play off my previous code.
function removeDuplicates(string:String):String {
return string.split('').sort().join('').replace(/(.)\1+/gi,'$1');
}

Benchmark on 10,000 runs in AS3

Yours from the post above: 1.0310000000000024 seconds
Mine from this comment: 0.48499999999999943 seconds

Once again, apologies for the misunderstanding and hopefully I didn’t mess it up again.

So what I needed is a string like “aabbccaaaaaddee” to be transformed to “abcde” (please note that there are two groups of “a“s in the first string and only one “a” in the resulting group).

Using “aabbccaaaaaddee” in your regular expression will give us the result “abcade” which is different from “abcde” (note the underlined letters). I need unique chars in the resulting string.

I tried with regular expression but there is no easy way (one step).

Thanks also for benchmarks. Great job.

var myPattern:RegExp = /(.)\1+/gi;
var str:String = "aaabbbcccddeeff";
trace(str.replace(myPattern, '$1'));