The readline function is what is used "behind the scenes" to implement the <> operator, and takes a typeglob, hence *KEYS instead of <KEYS>;

Keeping track of the min, max, total and count (for average value) may be faster than using the List utilities described earlier, or at least should take less memory, since you only need to keep track of a few values for each key. Although the utilities in question are extremely fast, you might need an array of thousands of values for each key, growing in size as you process the files.