Jean, Ista is right, but:
In your function you are asking as.Date to convert the whole data.frame df rather than just your daterep column. out<-ddply(d2, .(daterep), function(df) as.Date(strptime(df$daterep,format='%Y%m%d'))) >str(out) 'data.frame': 30 obs. of 2 variables: $ daterep: num 20100801 20100802 20100803 20100804 20100805 ... $ V1 : Date, format: "2010-08-01" "2010-08-02" "2010-08-03" "2010-08-04" ... On Tue, Aug 23, 2011 at 3:16 PM, jjap <jean.plamon...@fpinnovations.ca>wrote: > Dear R-users, > > I am trying to get the plyr syntax right, without much success. > > Given: > d<- data.frame(cbind(x=1,y=seq(20100801,20100830,1))) > names(d)<-c("first", "daterep") > d2<-d > > # I can convert the daterep column in place the classic way: > d$daterep<-as.Date(strptime(d$daterep, format="%Y%m%d")) > > # How to do it the plyr way? > ddply(d2, c("daterep"), function(df){as.Date(df, format="%Y%m%d")}) > # returns: Error in as.Date.default(df, format = "%Y%m%d") : > # do not know how to convert 'df' to class "Date" > > Thanks for any hints, > > ---jean > > -- > View this message in context: > http://r.789695.n4.nabble.com/ddply-how-to-transform-df-column-in-place-tp3764037p3764037.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. > [[alternative HTML version deleted]] ______________________________________________ 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.