I remain confused by the difference between library(MASS) data(Cars93)
as.data.frame(tapply(Cars93$Price,list(Cars93$Origin,Cars93$AirBags,Cars93$Passengers),median)) as.data.frame.table(tapply(Cars93$Price,list(Cars93$Origin,Cars93$AirBags,Cars93$Passengers),median)) I clearly want the latter, but that's not clear from the documentation. Best, Michael On Wed, Nov 25, 2009 at 5:55 PM, David Winsemius <dwinsem...@comcast.net> wrote: > > On Nov 25, 2009, at 4:11 PM, Michael Ash wrote: > >> Dear all, >> >> This seems to be working, but I'd like to make sure that I'm not doing >> anything wrong. >> >> I am using by() to construct a complicated summary statistic by >> several factors in my data (specifically, the 90-50 income ratio by >> city and race). >> >> cityrace.by <- by(microdata, list(microdata$city,microdata$race), >> function (x) quantile(x$income, probs=0.9) / quantile(x$income, >> probs=0.5) ) >> >> I would now like to use the data created by by() as a dataset with >> city-race as the unit of observation. >> >> However, cityrace.data <- as.data.frame(cityrace.by) does not work because >> "Error in as.data.frame.default(city.by) : >> cannot coerce class "by" into a data.frame" >> >> The following is not a documented use of as.data.frame.table(), but it >> seems to work. It gives the columns slightly strange names, including >> "Freq" for the statistic computed in by by() but otherwise, the >> dataframe is indexed by city and race with the 90-50 ratio as the >> variable >> >> cityrace.data <- as.data.frame.table(cityrace.by) > > If the by-object you get happens to be a 2d array, then why not. Tables are > matrices after all. > >> tt <- table(c(1,1), c(1,1)) >> tt > > 1 > 1 2 >> is.matrix(tt) > [1] TRUE > >> -- > > > David Winsemius, MD > Heritage Laboratories > West Hartford, CT > > -- Michael Ash, Associate Professor of Economics and Public Policy Department of Economics and CPPA University of Massachusetts Amherst, MA 01003 Tel +1-413-545-6329 Fax +1-413-545-2921 Email m...@econs.umass.edu http://people.umass.edu/maash ______________________________________________ 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.
