Hi sundialsvc4,

I think that in my approach to this problem I would “flip” it: let the second file drive the show, not the first!

Since your first file appears to contain nothing other than a list of “keys of interest,” let’s start the show by a simple loop that adds each key to a hash with a do-nothing value.

Just in case you didn't notice, that's exactly the approach suggested earlier by both poj and myself. I even explicitly explained that there were two possible approaches and that, in this case, it was probably a bit better to store the keys taken from the first file in the hash. Although, to tell the truth, choosing between the two approaches would require to know more about the respective size of the files. If the second file is much shorter than the first one, it might be better to choose the other way around.