Yes, I meant something like one of these: b <- aggregate(a$payday, list(a$name), max) b$x <- as.Date('1970-01-01') + b$x or b$x <- as.Date(b$x, origin='1970-01-01')
Thanks. -----Original Message----- From: David Winsemius [mailto:dwinsem...@comcast.net] Sent: Monday, November 22, 2010 3:58 PM To: Tan, Richard Cc: r-help@r-project.org Subject: Re: [R] aggregate a Date column does not work? On Nov 22, 2010, at 3:54 PM, Tan, Richard wrote: > Thanks, add as.Date('1970-01-01') to the result column works. But that should make them all the same date in 1970. Since aggregate renames the date column to "x", this should work: as.Date( aggregate(a$payday, list(a$name), max)$x ) [1] "2000-01-01" "1999-01-01" > > Richard > > -----Original Message----- > From: David Winsemius [mailto:dwinsem...@comcast.net] > Sent: Monday, November 22, 2010 3:51 PM > To: Tan, Richard > Cc: r-help@r-project.org > Subject: Re: [R] aggregate a Date column does not work? > > > On Nov 22, 2010, at 3:39 PM, Tan, Richard wrote: > >> Hi, I am trying to aggregate max a Date type column but have weird >> result, how do I fix this? > > In the process of getting max() you coerced the Dates to numeric and > now you need to re-coerce them back to Dates > > ?as.Date > as.Date(<your result>) (possibly with an origin it the default > "1970-01-01" doesn't get used. > > -- > David. >> >> >> >>> a <- rbind( >> >> + data.frame(name='Tom', payday=as.Date('1999-01-01')), >> >> + data.frame(name='Tom', payday=as.Date('2000-01-01')), >> >> + data.frame(name='Pete', payday=as.Date('1998-01-01')), >> >> + data.frame(name='Pete', payday=as.Date('1999-01-01')) >> >> + ) >> >>> a >> >> name payday >> >> 1 Tom 1999-01-01 >> >> 2 Tom 2000-01-01 >> >> 3 Pete 1998-01-01 >> >> 4 Pete 1999-01-01 >> >>> aggregate(a$payday, list(a$name), max) >> >> Group.1 x >> >> 1 Tom 10957 >> >> 2 Pete 10592 >> >> >> >> Thanks, >> >> Richard >> >> >> >> >> [[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. > > David Winsemius, MD > West Hartford, CT > > David Winsemius, MD West Hartford, CT ______________________________________________ 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.