I guess you could code you own function for average, seems simple enough.
func average(a, b):
return (a + b) / 2.0
If you need to average a variable amount of items you can do that with an array.
func average(arr):
var sum = 0
for item in arr:
sum += item
return sum / arr.size()
I didn't test the code, but I believe that should work.