Using this test data, say: dd <- Sys.Date() + 0:9 fac <- gl(5,2)
Try this: do.call("c", tapply(dd, fac, max, simplify = FALSE)) or if a list result is ok then just tapply(dd, fac, max, simplify = FALSE) Another possibility using the as.Date.numeric method in the zoo package is: library(zoo) as.Date(tapply(dd, fac, max)) For more info on the internal representation of "Date" class objects see the Help desk article in R News 4/1. On 1/30/06, David Randel <[EMAIL PROTECTED]> wrote: > I have a column in a data frame that has a class of "Date" and a mode of > "numeric". When I: > > max(df$Date) > > My output stays in Date format, i.e. "2006-01-03". > > However, when I run the following statment: > > tapply(df$Date, df$SomeFactor, max) > > my output looks like this: 9129 9493 9861 10226 10591 10956 11320 > 11687 12052 12417 > > The returned object is of mode "numeric" and class "array". Each array > element is of mode "numeric" and class "numeric". I believe that this is > the integer representation of my date. I can't seem to convert it back to a > date. > > How do I get these to be intrepreted as a date instead of a number? > > Thanks, > ~Dave R. > > ______________________________________________ > 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