Check the *apply() series of functions. tapply() will do what you want. attach(mtcars) tapply(hp,list(cyl,gear),mean)
HTH, Daniel Mark Alen wrote: > > I know commands like xtabs and table allow a user to do cross-tabulation > For example the following command generates a pivot table that shows the > number of cars that have the same number of gears and cylinders. > >>xtabs(~cyl+gear,data =mtcars) > gear > cyl 3 4 5 > 4 1 8 2 > 6 2 4 1 > 812 0 2 >> > > We can extend the formula so it could show the sum of the horse power for > the cars in each bin > >>xtabs(hp~cyl+gear,data =mtcars) > gear > cyl 3 4 5 > 4 97 608 204 > 6 215 466 175 > 82330 0 599 >> > > I am now wondering, is it possible to calculate the mean of horse powers > for cars in each bin? for example something like > this xtabs(mean(hp)~cyl+gear, data = mtcars) > > Thank you > Mark > > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- View this message in context: http://r.789695.n4.nabble.com/Calculating-the-mean-of-values-in-tables-using-formulae-tp3688416p3688437.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
