在R中将日期转换为星期几

Question

可能重复：
在R中查找星期几

我有一些日期数据，例如11-01-2011。但我想要添加相应的星期几，如星期一、星期二等。是否有包含日期和星期几信息的R包？

- Ikuyasu

Answer 1

weekdays(as.Date('16-08-2012','%d-%m-%Y'))
[1] "Thursday"

- Roland

---

我总是忘记weekdays()是在基础R中的。+1 - A5C1D2H2I1M1N2O1R2T1

Answer 2

lubridate 包非常适合处理这种任务。

> wday(as.Date('16-08-2012','%d-%m-%Y'))
[1] 5
> wday(as.Date('16-08-2012','%d-%m-%Y'), label=TRUE)
[1] Thurs
Levels: Sun < Mon < Tues < Wed < Thurs < Fri < Sat
> wday(as.Date('16-08-2012','%d-%m-%Y'), label=TRUE, abbr = FALSE)
[1] Thursday
Levels: Sunday < Monday < Tuesday < Wednesday < Thursday < Friday < Saturday

- A5C1D2H2I1M1N2O1R2T1

Answer 3

这里有一些信息，可以帮助您创建自己的库或例程

常量：

day_of_month

    the day of the month
    e.g. if input mm-dd-yyy then dd

月份:

march = 1
april = 2
may = 3
...

年份

yy[yy]  (last to digits from yyyy)
   *subtract 1 if month jan or feb
    e.g. if input date is 02-01-2012 (mm-dd-yyyy)
         year =  (12-1) = 11

世纪

[yy]yy  (first two digits from yyyy)
     e.g. if input year is 2012 then 20 = century
     * year 2000, 1900, ... are 20-1, 19-1 respectively

算法

step1: floor(century / 4)

step2: year

step3: floor(year/4)

step4: floor(month*2.6 -0.2)  #this is the leap year correction

step5: day_of_month

step6: add step1...step5

step7: divide by 7  # modulo 7 in codespeak

step8: the remainder is the day of the week

解释结果：

Sun = 0, Mon = 1, Tues = 3, etc..

这不是一个库，但就像公共服务的广告词所说...

"阅读：知道得越多，你就会更了解"

参考资料：http://www.faqs.org/faqs/sci-math-faq/dayWeek/

- JCR000