Wow! That's very elegant and simple. I initially thought using hash tables would be beneficial, but I thought that since there would be multiple chromosome numbers as the key that it wouldn't work.

You've definitely pointed me in the right direction and I thank you for helping me with this problem that I got stuck on.

One question regarding the Data::Dump. I don't have the module installed on my computer (and I'm not sure if its on the server I'm working on), but I #commented it out and the solution still worked. Just as a precaution, is the module necessary to produce the correct output? I only ask because this was a small sample input I'm working with but the actual data set is 15GB. I just want to make sure before I even attempt that beast.

Thank you,

a217