2-8 R语言基础 日期与时间

#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