Hmm, Moritz explained you a specific mistake to be corrected. But Choroba told you something that you should not overlook and is at least as important in my view: load the param file into memory (a hash or whatever, depending on the specifics), but don't load the data file in memory if you can avoid it. It is usually far better to iterate over the data line by line when possible. This will save your day when your datafile becomes huge.