R - dates with lubridate

datetime

Table of Contents

• 1 package lubridate
  
  • 1.1 reading dates with lubridate
  • 1.2 working with dates

1 package lubridate

1.1 reading dates with lubridate

• lubridate is a relatively new package which allows to handle date and date time formats in a more convenient way than it was possible with format()
  
• first load the package
  

library(lubridate)

• if you want to read date or convert some data into date/date time format you can use ymd()
  
• the first argument to ymd() have to be numeric oder string vector of suspected dates
  
• it should be used if there is a year, month and time component in a arbitry order, seperated by one of the following seperators: "-", "/", ".", and ""
  
• analogous ymd should appear in one of the following order: ymd, ydm, mdy, myd, dmy, dym
  
• there is a optional argument tz to specify which time zone to parse the date with (string, known by the OS)
  

ydm(12051103) # ->  "1205-03-11 UTC"
ymd(12051103) # ->  "1205-11-03 UTC"
dym(12051103) # ->  "511-03-12 UTC"
dmy(12051103) # ->  "1103-05-12 UTC"
mdy(12051103) # ->  "1103-12-05 UTC"
myd(12051103) # ->  "511-12-03 UTC"

[1] "1205-03-11 UTC"
[1] "1205-11-03 UTC"
[1] "511-03-12 UTC"
[1] "1103-05-12 UTC"
[1] "1103-12-05 UTC"
[1] "511-12-03 UTC"

• it can also deal with the year consisting of two digits
  

dym(120503) # -> "2005-03-12 UTC"
dym(127503) # -> "1975-03-12 UTC"

[1] "2005-03-12 UTC"
[1] "1975-03-12 UTC"

• extract information:
  
  • day
    

my.date <- dym(120503)
day(my.date)

[1] 12

• week day (number)
  

wday(my.date)

[1] 7

• week day (string)
  

wday(my.date,label=T)

[1] Sat
Levels: Sun < Mon < Tues < Wed < Thurs < Fri < Sat

• year
  

year(my.date)

[1] 2005

• month (number)
  

month(my.date)

[1] 3

• month (name of month)
  

month(my.date,label=T)

[1] Mar
12 Levels: Jan < Feb < Mar < Apr < May < Jun < Jul < Aug < Sep < ... < Dec

• week
  

week(my.date)

[1] 11

• day of year
  

yday(my.date)

[1] 71

1.2 working with dates

• get the origin of the current time scale
  

origin

[1] "1970-01-01 GMT"

• get the current date
  

x <- today()
x

[1] "2012-03-17"

• week of current day
  

week(x)

• two weeks later
  

week(x) <- week(x) + 2
x

• is also a Saturday
  

wday(x,label=T)

 [1] Sat
Levels: Sun < Mon < Tues < Wed < Thurs < Fri < Sat

• rounding: floor_date(), ceiling_date()
  
  • rounding down and up to the nearest integer day value
    

floor_date(my.date,"day")     # -> "2005-03-12 UTC" 
ceiling_date(my.date,"day")   # -> "2005-03-13 UTC"

[1] "2005-03-12 UTC"
[1] "2005-03-13 UTC"

• rounding down and up to the nearest integer month value
  

floor_date(my.date,"month")     # ->  "2005-03-01 UTC"
ceiling_date(my.date,"month")   # ->  "2005-04-01 UTC"

[1] "2005-03-01 UTC"
[1] "2005-04-01 UTC"

• rounding down and up to the nearest integer year value
  

floor_date(my.date,"year")     # ->  "2005-01-01 UTC"
ceiling_date(my.date,"year")   # ->  "2006-01-01 UTC"

[1] "2005-01-01 UTC"
[1] "2006-01-01 UTC"

• is a year a leap-year (argument has to be a date)
  

leap_year(ymd("20000101"))

• create a time interval given start and end point
  

date1 <- ymd("2000-01-01")
date2 <- ymd("2000-10-01")
my.int <- new_interval(date1,date2)
my.int

[1] 2000-01-01 UTC--2000-10-01 UTC

• check whether or not a date falls within an interval
  

date3 <- ymd("2001-01-02")
date3 %within% my.int

[1] FALSE

or

date4 <- ymd("2000-06-02")
date4 %within% my.int

[1] TRUE

• check whether or not an interval falls within an interval
  

my.int2 <- new_interval(date1,date4)
my.int2 %within% my.int

[1] TRUE

Date: 2012-03-17 12:42:50 CET

Author: Mandy

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