Rate of Change from a Data Matrix

I was able to extract the data based on the identifier in row 0. I want to calculate a rate of change based on dates in row 2 for values found in rows 4 to 12. I will also calculate rates of change from the most recent date on all previous dates. I read over the papers on indexes and range variables so I don't think I change the range variable for data set comparisons. I was able to calculate the rate of change by separating out each data set into vectors but this sounds messy. Hopefully your answer with allow me to solve other pending questions for data analysis. Thanks