转 http://stackoverflow.com/questions/1962278/dealing-with-timestamps-in-r
You want the (standard) POSIXt type from base R that can be had in ‘compact form‘ as a POSIXct (which is essentially a double representing fractional seconds since the epoch) or as long form in POSIXlt (which contains sub-elements). The cool thing is that arithmetic etc are defined on this -- see help(DateTimeClasses)
Quick example:
R> now <- Sys.time() R> now [1] "2009-12-25 18:39:11 CST" R> as.numeric(now) [1] 1.262e+09 R> now + 10 # adds 10 seconds [1] "2009-12-25 18:39:21 CST" R> as.POSIXlt(now) [1] "2009-12-25 18:39:11 CST" R> str(as.POSIXlt(now)) POSIXlt[1:9], format: "2009-12-25 18:39:11" R> unclass(as.POSIXlt(now)) $sec [1] 11.79 $min [1] 39 $hour [1] 18 $mday [1] 25 $mon [1] 11 $year [1] 109 $wday [1] 5 $yday [1] 358 $isdst [1] 0 attr(,"tzone") [1] "America/Chicago" "CST" "CDT"
As for reading them in, see help(strptime)
As for difference, easy too:
R> Jan1 <- strptime("2009-01-01 00:00:00", "%Y-%m-%d %H:%M:%S") R> difftime(now, Jan1, unit="week") Time difference of 51.25 weeks
Lastly, the zoo package is an extremely versatile and well-documented container for matrix with associated date/time indices.
原文：http://www.cnblogs.com/shalijiang/p/4523863.html