you could use something like by(data, list(data1$day, data1$hour), function(x) cor(x[,"var1"], x[, "var2"]))
This will return a list and then you can unlist and turn to matrix HTH > Is there a way to apply a function, say cor(), to each combination of some > number of variables, and this, without using loops? > > For example, I have day, hour, var1 and var2. How could I compute > cor(var1,var2) for each day*hour combination and obtain a matrix with day, > hour and the cor value for each combination? > > Thanks for your time, > > Marc > > ==================Marc Bélisle > Professeur adjoint > Chaire de recherche du Canada en écologie spatiale et en écologie du > paysage > Département de biologie > Université de Sherbrooke > 2500 Boul. de l'Université > Sherbrooke, Québec > J1K 2R1 Canada > > Tél: +1-819-821-8000 poste 1313 > Fax: +1-819-821-8049 > Courriél: [EMAIL PROTECTED] > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@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 > ______________________________________________ R-help@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