[R] Matrix of Index Variables

[Jason Turner]

TyagiAnupam at aol.com wrote:

> What is a good way to create a matrix of index variables based on all 
> possible combinations of a list of factors in a data-frame, say list(age, sex)? "age" 
> and "sex" are numeric and factor variables in a dataframe, with 99 and 2 
> values, respectively.
> I would like to use these for subsetting the data-frame, apply functions to 
> subset and collecting the results.
> 

Rather than creating a new index, I think you want the function "by()". 
  Something like

foo <- by(mydata,list(age=mydata$age, sex=mydata$sex), 
your.summary.function)

Cheers

Jason
-- 
Indigo Industrial Controls Ltd.
http://www.indigoindustrial.co.nz
64-21-343-545
jasont at indigoindustrial.co.nz