Make sure your function works for the "2d" array [[1]]

This fails for "1.2.3.4.444"

I'm assuming the goal of this kata is algorithmic optimization and not semantic interpretation, so I think the example could be made less ambiguous in my opinion:

largestDifference([1,2,3]); //returns 2 since data[0] <= data[2], therefore 2-0 = 2