Hi, First up, thanks again for all the help I'm getting on this list. I'm making great headway in analyzing my experimental data on an experiment by experiment basis. No way I could have done this in the time I've done it without your help. This email is partially a question about R but is also soliciting overall guidance if anyone wants to give it. I somehow managed to get an electrical engineering degree decades ago from the University of California system without ever being required to take a statistics class so in that area I'm lacking background. Maybe there's a good subject someone can point me toward. (Keep it simple though!) OK, I've now got dozens of experiments sitting in individual data.frames. In most cases the data.frames look more or less like the example below - Experiment Start time down the left side, Experiment Completion time across the top and results in the cells. The following data started at 830 and is 3 minute data so the first measurement came at 833, then 836, etc. EnTime 836 842 845 848 851 854 900 903 1 833 -386 0 -772 -938 -772 0 -386 2 836 0 -386 0 0 0 -246 714 -632 3 839 0 0 0 0 -386 0 0 -772 4 842 0 0 -386 0 0 0 -682 0 5 845 0 0 0 0 0 0 0 0 6 848 0 0 0 0 -386 0 0 0 7 851 0 0 0 0 0 0 0 0 8 854 0 0 0 0 0 0 -386 0 9 857 0 0 0 0 0 0 0 0 10 900 0 0 0 0 0 0 0 0 11 903 0 0 0 0 0 0 The issue I'm thinking about now is how to compare experiments when the time increment for each is different? This one is 3 minutes, others are 1 minute, 5 minutes, 13 minutes, etc. My initial thought is to try and roll things up into common sizes, like 30 minute or 60 minute chunks. Granted, I won't get the same number of measurements in each chunk, but it's a start and would yield a data.frame that's easy to view in the Rgui console so I'd be happy with that, but is that a good method in terms of the statistics of the problem? should I be paying attention to the number of experiments, maybe as a percentage of the whole, or something else? I don't know. Anyway, I'd like to try rolling this data up by time increment to start and I'm wondering if there any easy ways to do that? Taking 15 minute increments I would like to get something like EnTime 845 900 915 1 845 SUM SUM SUM 2 900 SUM SUM SUM 4 915 SUM SUM SUM where the SUM is the sum of the pieces making up this new cell. I tried using subset but apparently it doesn't work on arrays like this, telling me that EnTime>=830 isn't valid for factors. I can certainly find ways to munge the data set, changing EnTime values but that seems like stuff I shouldn'y be doing. that said it's pretty easy to do I suspect. (Modulo 15, etc.) Is there a way to use cast() to grab time increments. Instead of cast(Results, EnTime ~ ExTime, ...) returning by the exact value, can cast collect values together in groups? Any ideas appreciated before I start banging away at doing my less interesting methods. Thanks, Mark