#日期 Date
> x<-date()
> class(x)
[1] "character"
> x2 <- Sys.Date()
> class(x2)
[1] "Date"
> x3<-as.Date("2018-11-03")
> class(x3)
[1] "Date"
> weekdays(x3) #星期
[1] "星期六"
> months(x3) #月份
[1] "十一月"
> quarters(x3) #季度
[1] "Q4"
> julian(x3) #距离1970-01-01有多少天
[1] 17838
attr(,"origin")
[1] "1970-01-01"
> x4 <- as.Date("2018-11-01")
> x4-x3
Time difference of -2 days
> as.numeric(x4-x3)
[1] -2
> #时间 Time
> x <- Sys.time()
> class(x)
[1] "POSIXct" "POSIXt"
> y <- as.POSIXct(x)
> y
[1] "2018-11-11 15:07:57 CST"
> z <- as.POSIXlt(x)
> z
[1] "2018-11-11 15:07:57 CST"
> names(unclass(z))
[1] "sec" "min" "hour" "mday" "mon" "year" "wday" "yday" "isdst"
[10] "zone" "gmtoff"
> z$sec
[1] 57.64549
> as.POSIXct(z)
[1] "2018-11-11 15:07:57 CST"
> as.Date("2018-01-01")
[1] "2018-01-01"
> x1 <- "Jan 1,2018 01:01"
> strptime(x1,"%B %d, %Y %H:%M")
[1] NA