In PHP there is a very useful function called array_count_values. It sorts an array by returning a 2 dimensional array consisting of non duplicate elements as keys, and values determined by how many times these elements appeared in the original array.

update 09.10.10

This can be achieved (in AS2 and AS3) in a much simpler manner, using the following function or prototype:

Array.prototype.countValues = function() : Array
{
	var i, j = -1, c, o = {}, r = [], v, n = a.length;
	for(i = 0;i < n;++i) (c = o[v = a[i]]) ? ++c[1] : r[int(++j)] = o[v] = [v,1];
	return r;
}

So, for example, an array [“red”,”green”,”blue”,”red”] would be converted into [“red” => 2, “green” =>1, “blue” => 1]. Duplicate elements are removed and the new array indicates how many times each, now unique value occurred in the array.

Unfortunately, Actionscript has no such function built in, so I made one. It is a modification of Senocular’s array.unique() prototype (which you can find in his Actionscript library), however rather than simply returning a unique array, it returns the 2 dimensional array mentioned above. Read : AS2 Array count values »