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 [EMAIL PROTECTED]
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