Numeric And Non Numeric Data?

I am reading a data file and storing them in an array of string.Data is random, could be like "1","2","133,18" but sometimes there can be missing values like "?".Once I load the data in the array, I want to check if at least a majority (like 60% of them) are numeric values.If yes, then I wanna track down the higher and lowest value in the array, and output a range of 5.Loop through the array

If 60% of them are numbers (integers or decimals) then find highest value, find lowest value end if produce range

If for example lowest = 1 and highest = 100, range of 5 means 0,20,40,60,80,100 (so 5 ranges are 0-20, 20-40, 40-60, 60-80, 80-100).Also if the ranges turn to have decimals due to weird numbers, I would like to round them up.My problem is, in order to find highest and lowest when there are non numeric values in the array like "?", how should I handle those? I was thinking of something like Double.NaN but I would have to have an array of doubles.