I don't believe there is (if you are talking about the middle of a list of numbers). A quick look shows that Haxe doesn't have that function built in (from what I can see), but you can sort the list (temporarily) and then pick the number at the middle of the list.
Try importing in this behaviour I just wrote and seeing if it works the way you want it to (it includes a global custom block). The file is a png but contains a behaviour - just import it and see.