Dear all, I'm wanting to do a series of comparisons among 4 categorical variables: a <- aggregate(y, list(var1, var2, var3, var4), sum) This gets me a very nice 2-dimensional data frame with one column per variable, BUT, as help for aggregate says, <<empty subsets are removed>>. I don't see in help(aggregate) how I can change this. In contrast, a <- tapply(y, list(var1, var2, var3, var4), sum) gives me results for everything including empty subsets, but in an awkward 4-dimensional array that takes me another 10 lines of inefficient code to turn into a 2D data.frame. Is there a way to directly do this calculation INCLUDING results for empty subsets, and still obtain a 2D array, matrix, or data.frame? OR alternatively is there a simple way to mush the 4D result from the tapply into a 2D matrix/data.frame? thanks very much in advance for any help! -jlb
************************************ Joseph P. LeBouton Forest Ecology PhD Candidate Department of Forestry Michigan State University East Lansing, Michigan 48824 Office phone: 517-355-7744 email: lebouton at msu.edu