Hi Cristian, instead of aggregate, how about something like:
n <- dim(my_agg)[1] my_agg$vol.diff <- my_agg$Vol - c(NA, my_agg$Vol[1:(n-1)] my_agg <- my.agg[my.agg$Age > min(my.agg$Age),] (assumes same minimum age for all treatments) (not checked) Cheers, Andrew On Thu, Nov 01, 2007 at 12:09:34PM -0400, [EMAIL PROTECTED] wrote: > Hi everyone > > I am trying to summarize a table with yield estimates of a forest > plantation. For that I have four blocks and four treatments measured over > a period of 10 years (every year). In each plot trees are measured > (diameters and heights). > > With aggregate function I can calculate the average diameter or the total > volume for each plot at any time with something like this: > > my_agg <- aggregate(list(Ht = HTO, Dbh = DBH), list(Age = AGE, Block = > BLOCK, Treat = TREAT), sum) > > my_agg <- aggregate(list(VOL = VOLUME), list(Age = AGE, Block = BLOCK, > Treat = TREAT), sum) > > where HTO is the height of the tree > Ht average height of trees in each plot at time t > DBH is the diameter at 1.3 meter height > Dbh is the average diameter of the plot at time t > VOL is the [i]th tree volume > Vol is the volume of the plot at time t > > To do actual growth analysis I need to calculate the difference in volume > between t and (t-1) for every block/treatment. > > Now the question > > How can I use aggregate to calculate the difference of each time series > and have an output like aggregate does? I know it is imposible to use > diff() within aggregate because it gives me an scalar. > In SAS proc means handles such a thing, and diff() in R is fine for a > single series, but in this case I want to calculate for all the > treatments/blocks at the same time. > > I can do the whole using by and some more less elegant procedures, but I > figure there should be a cleaner way as in PROC MEANS. > > Any suggestions? > > Cristian Montes > NC State University > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- Andrew Robinson Department of Mathematics and Statistics Tel: +61-3-8344-9763 University of Melbourne, VIC 3010 Australia Fax: +61-3-8344-4599 http://www.ms.unimelb.edu.au/~andrewpr http://blogs.mbs.edu/fishing-in-the-bay/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
