.. One issue with the solution proposed by Jeff is that the transformed column does not have the original's type:
> x = structure(list(time = structure(c(1020232904.818, 1020232904.818 ), class = c("POSIXt", "POSIXct"), tzone = ""), price = c(321, 323.5), minute = c(1020232860, 1020232860)), .Names = c("time", "price", "minute"), row.names = 1:2, class = "data.frame") minute <- function(t) { d <- as.POSIXlt(t, origin = as.Date("1970-01-01")) d$sec <- 0 as.POSIXct(d) } > x$minute = sapply(x$time, minute) > head(x) time price minute 1 2002-05-01 07:01:44 321.0 1020232860 2 2002-05-01 07:01:44 323.5 1020232860 > class(x.l$minute) [1] "numeric" -- View this message in context: http://r.789695.n4.nabble.com/Lost-in-POSIX-tp3052768p3163969.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.