[R] Calculate aggregate differences
Andrew Robinson
A.Robinson at ms.unimelb.edu.au
Thu Nov 1 17:23:04 CET 2007
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, crmontes at ncsu.edu 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
>
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--
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/
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