R实战：【基本类型】日期类型POSIXlt、Date
R实战系列专栏
介绍
POSIXlt、Date是时间序列类型的索引类型，也是R的基础类型，有大量的操作可以方便的处理日期。
POSIXct格式
R中，从文本文件加载数据自动使用该类型
POSIXct格式的时间：以有符号整数形式存储，表示从1970-01-01到该时间点经过的秒数
POSIXlt格式的时间：以字符串形式存储，包含年月日等
"05/27/84" 对应格式 "%m/%d/%y"
"May 27 1984" 对应格式 "%B %d %Y"
> as.POSIXlt('2016/04/05')
[1] "2016-04-05 CST"
http://blog.csdn.net/u014801157/article/details/52879483
Date的创建
> dts <- as.Date("20050101", '%Y%m%d') + seq(0,1000,15)
> dts
[1] "2005-01-01" "2005-01-16" "2005-01-31" "2005-02-15" "2005-03-02"
[6] "2005-03-17" "2005-04-01" "2005-04-16" "2005-05-01" "2005-05-16"
[11] "2005-05-31" "2005-06-15" "2005-06-30" "2005-07-15" "2005-07-30"
[16] "2005-08-14" "2005-08-29" "2005-09-13" "2005-09-28" "2005-10-13"
[21] "2005-10-28" "2005-11-12" "2005-11-27" "2005-12-12" "2005-12-27"
[26] "2006-01-11" "2006-01-26" "2006-02-10" "2006-02-25" "2006-03-12"
[31] "2006-03-27" "2006-04-11" "2006-04-26" "2006-05-11" "2006-05-26"
[36] "2006-06-10" "2006-06-25" "2006-07-10" "2006-07-25" "2006-08-09"
[41] "2006-08-24" "2006-09-08" "2006-09-23" "2006-10-08" "2006-10-23"
[46] "2006-11-07" "2006-11-22" "2006-12-07" "2006-12-22" "2007-01-06"
[51] "2007-01-21" "2007-02-05" "2007-02-20" "2007-03-07" "2007-03-22"
[56] "2007-04-06" "2007-04-21" "2007-05-06" "2007-05-21" "2007-06-05"
[61] "2007-06-20" "2007-07-05" "2007-07-20" "2007-08-04" "2007-08-19"
[66] "2007-09-03" "2007-09-18"
> str(dts)
Date[1:67], format: "2005-01-01" "2005-01-16" "2005-01-31" "2005-02-15" ...Date的加减法运算
日期Date加上一个整数n之后是n天之后，减法对应n天之前
dayWidth<-30
>
> buyDate<-as.Date('20170405','%Y%m%d')
> saleDate<-as.Date('20170509','%Y%m%d')
>
> buyDate
[1] "2017-04-05"
> saleDate
[1] "2017-05-09"
>
> oneYearBefore<-buyDate - dayWidth
> oneYearLater<-saleDate + dayWidth
>
> oneYearBefore
[1] "2017-03-06"
> oneYearLater
[1] "2017-06-08"
>
> x<-oneYearLater - oneYearBefore
> as.intdayWidth<-30
>
> buyDate<-as.Date('20170405','%Y%m%d')
> saleDate<-as.Date('20170509','%Y%m%d')
>
> buyDate
[1] "2017-04-05"
> saleDate
[1] "2017-05-09"
>
> oneYearBefore<-buyDate - dayWidth
> oneYearLater<-saleDate + dayWidth
>
> oneYearBefore
[1] "2017-03-06"
> oneYearLater
[1] "2017-06-08"
>
> x<-oneYearLater - oneYearBefore
> as.integer(x)
[1] 94Date格式化转换
%a
Abbreviated weekday name in the current locale. (Also matches full name on input.)
%A
Full weekday name in the current locale. (Also matches abbreviated name on input.)
%b
Abbreviated month name in the current locale. (Also matches full name on input.)
%B
Full month name in the current locale. (Also matches abbreviated name on input.)
%c
Date and time, locale-specific.
%d
Day of the month as decimal number (01–31).
%H
Hours as decimal number (00–23).
%I
Hours as decimal number (01–12).
%j
Day of year as decimal number (001–366).
Abbreviated weekday name in the current locale. (Also matches full name on input.)
%A
Full weekday name in the current locale. (Also matches abbreviated name on input.)
%b
Abbreviated month name in the current locale. (Also matches full name on input.)
%B
> dayWidth<-30
>
> buyDate<-as.Date('20170405','%Y%m%d')
> saleDate<-as.Date('20170509','%Y%m%d')
>
> buyDate
[1] "2017-04-05"
> saleDate
[1] "2017-05-09"
>
> oneYearBefore<-buyDate - dayWidth
> oneYearLater<-saleDate + dayWidth
>
> oneYearBefore
[1] "2017-03-06"
> oneYearLater
[1] "2017-06-08"Full month name in the current locale. (Also matches abbreviated name on input.)
%c
Date and time, locale-specific.
%d
Day of the month as decimal number (01–31).
%H
Hours as decimal number (00–23).
%I
Hours as decimal number (01–12).
%j
Day of year as decimal number (001–366).
日期在一年中的索引(字符串类型，需要转换为整数)
%m
Month as decimal number (01–12).
%M
Minute as decimal number (00–59).
%p
AM/PM indicator in the locale. Used in conjuction with %I and not with %H.
%S
Second as decimal number (00–61), allowing for up to two leap-seconds (but POSIX-compliant OSes will ignore leap seconds).
%U
Week of the year as decimal number (00–53) using the first Sunday as day 1 of week 1.
%w
Weekday as decimal number (0–6, Sunday is 0).
%W
Week of the year as decimal number (00–53) using the first Monday as day 1 of week 1.
%x
Date, locale-specific.
%X
Time, locale-specific.
%y
Year without century (00–99). If you use this on input, which century you get is system-specific. So don't! Often values up to 69 (or 68) are prefixed by 20 and 70(or 69) to 99 by 19.
%Y
Year with century. exg 1900-
%z
(output only.) Offset from Greenwich, so -0800 is 8 hours west of Greenwich.
%Z
(output only.) Time zone as a character string (empty if not available).
%m
Month as decimal number (01–12).
%M
Minute as decimal number (00–59).
%p
AM/PM indicator in the locale. Used in conjuction with %I and not with %H.
%S
Second as decimal number (00–61), allowing for up to two leap-seconds (but POSIX-compliant OSes will ignore leap seconds).
%U
Week of the year as decimal number (00–53) using the first Sunday as day 1 of week 1.
%w
Weekday as decimal number (0–6, Sunday is 0).
%W
Week of the year as decimal number (00–53) using the first Monday as day 1 of week 1.
%x
Date, locale-specific.
%X
Time, locale-specific.
%y
Year without century (00–99). If you use this on input, which century you get is system-specific. So don't! Often values up to 69 (or 68) are prefixed by 20 and 70(or 69) to 99 by 19.
%Y
Year with century. exg 1900-
%z
(output only.) Offset from Greenwich, so -0800 is 8 hours west of Greenwich.
%Z
(output only.) Time zone as a character string (empty if not available).
format日期转换为字符串
> dt <- as.Date("20050101", '%Y%m%d')
> dt
[1] "2005-01-01"
> format(dt,'%Y')
[1] "2005"
> format(dt,'%j')
[1] "001"
> as.integer(format(dt,'%j'))
本文参考网址： http://astrostatistics.psu.edu/su07/R/html/base/html/strptime.html