Does this start to do what you want?
> x <- "NUM sim N
+ 1 1 466
+ 1 2 450
+ 1 3 473
+ 1 4 531
+ 1 5 515
+ 1 6 502
+ 1 7 471
+ 1 8 460
+ 1 9 458
+ 1 10 434
+ 2 1 289
+ 2 2 356
+ 2 3 387
+ 2 4 440
+ 2 5 457
+ 2 6 466
+ 2 7 467
+ 2 8 449
+ 2 9 387
+ 2 10 394
+ 3 1 367
+ 3 2 400
+ 3 3 476
+ 3 4 508
+ 3 5 478
+ 3 6 501
+ 3 7 513
+ 3 8 505
+ 3 9 492
+ 3 10 465"> a <- read.table(textConnection(x), header=T)
> lambda <- by(a, a$NUM, function(x) x$N[-1] / x$N[-length(x$N)])
> lambda
a$NUM: 1
[1] 0.9656652 1.0511111 1.1226216 0.9698682 0.9747573 0.9382470
0.9766454 0.9956522 0.9475983
------------------------------------------------------------------------------
a$NUM: 2
[1] 1.2318339 1.0870787 1.1369509 1.0386364 1.0196937 1.0021459
0.9614561 0.8619154 1.0180879
------------------------------------------------------------------------------
a$NUM: 3
[1] 1.0899183 1.1900000 1.0672269 0.9409449 1.0481172 1.0239521
0.9844055 0.9742574 0.9451220> # sum of lambdas
> sapply(lambda, sum)
1 2 3
8.942166 9.357799 9.263944> # mean
> sapply(lambda, mean)
1 2 3
0.993574 1.039755 1.029327> # sd
> sapply(lambda, sd)
1 2 3
0.05822850 0.10525335 0.08004527>
>
>
On 10/10/06, Bret Collier <bret at tamu.edu>
wrote:> R Users,
> I have written a small simulation model in R which outputs a datafile
consisting of ending population sizes for each simulation run (year). The data
(see short data example below) is labeled by NUM (simulation run), sim (year)
and N (yearly count). After searching the help files and coming up empty
(probably because I used the wrong terms) I am appealing for some help for
working with the output dataset.
>
> What I want to do is for each of the i simulation runs (NUM) I want to
>
> 1) take N(t+1)/N(t)=lambda(t) for each year (where in the below example
t=1,...,10--total years of the simulation)
> 2) Sum lambda(t) and divide by t (e.g., output both the mean/se of lambda
for each simulation run)
> 3) Take the mean of the mean(lambda's) (and associated stddev, min,
max) over all NUM
>
> I think I have to write a function for use within an apply statement, but I
am not quite there yet on the learning curve so most of my recent attempts in R
have been useful learning experiences of what not to do...
>
> Any suggestions/direction is greatly appreciated.
>
> Bret Collier
> TX A&M
>
> NUM sim N
> 1 1 466
> 1 2 450
> 1 3 473
> 1 4 531
> 1 5 515
> 1 6 502
> 1 7 471
> 1 8 460
> 1 9 458
> 1 10 434
> 2 1 289
> 2 2 356
> 2 3 387
> 2 4 440
> 2 5 457
> 2 6 466
> 2 7 467
> 2 8 449
> 2 9 387
> 2 10 394
> 3 1 367
> 3 2 400
> 3 3 476
> 3 4 508
> 3 5 478
> 3 6 501
> 3 7 513
> 3 8 505
> 3 9 492
> 3 10 465
>
> platform i386-pc-mingw32
> arch i386
> os mingw32
> system i386, mingw32
> status
> major 2
> minor 3.0
> year 2006
> month 04
> day 24
> svn rev 37909
> language R
> version.string Version 2.3.0 (2006-04-24) (yeah, I need to update)
>
> ______________________________________________
> R-help at stat.math.ethz.ch 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.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem you are trying to solve?