[R] Help using tapply with multiple variables

[Corey Sparks]

Dear list,
I have the function (as a simple example, which is actually part of a  
larger function)

pres.test<-function(N0=N0, N1=N1)
{
     dt<-5
     r<-log(N1/N0)/dt
     r
}

which calculates the annual growth rates in a population

Where N0 is the population classified into age intervals, say 5  
years, at time=1995, and N1 is the population by 5 year age classes  
at time=2000.

For example some data like this are:
country   pop1995 pop2000
1     1712    1940
1     1329    1535
1     1101    1268
1     911    1048
1      758     859
2      627     710
2      513     584
2      420     475
2     754     965
2     638     741

I want to use the tapply function to apply the pres.test function  
over all countries in my data table (the real data have ~150  
countries and 10 age classes), but I can't seem to get tapply to take  
as input to FUN more than one variable, for example I tried:

popdat<-cbind(dat2.sub$pop1995, dat2.sub$pop2000) #try to force the  
two time points into a vector form

tapply(popdat, dat2.sub$country, pres.test, ...=list(N0=popdat[,1],  
N1=popdat[,2])) #tried to pass the other arguments that pres.test  
needs  via ...

And got the error:
Error in tapply(popdat, dat2.sub$Country, pres.test, ... = list(N0 =  
popdat[,  :
   arguments must have same length

I see that the function mapply will take multiple arguements, but I  
don't think it will use an INDEX like tapply.

Any comments or clarification would be most appreciated.

Corey

-- 
Corey Sparks
Assistant Professor
Department of Demography and Organization Studies
University of Texas at San Antonio
One UTSA Circle
San Antonio, TX 78249
210-458-6858
corey.sparks at utsa.edu
https://rowdyspace.utsa.edu/users/ozd504/www/index.htm