R Language Date and Time
Introduction
R comes with classes for dates, date-times and time differences; see ?Dates, ?DateTimeClasses, ?difftime and follow the "See Also" section of those docs for further documentation. Related Docs: Dates and Date-Time Classes.
Remarks
Classes
-
A date-time class, POSIXct stores time as seconds since UNIX epoch on
1970-01-01 00:00:00 UTC. It is the format returned when pulling the current time withSys.Time(). -
A date-time class, stores a list of day, month, year, hour, minute, second, and so on. This is the format returned by
strptime. -
Date The only date class, stores the date as a floating-point number.
Selecting a date-time format
POSIXct is the sole option in the tidyverse and world of UNIX. It is faster and takes up less memory than POSIXlt.
origin = as.POSIXct("1970-01-01 00:00:00", format ="%Y-%m-%d %H:%M:%S", tz = "UTC")
origin
## [1] "1970-01-01 UTC"
origin + 47
## [1] "1970-01-01 00:00:47 UTC"
as.numeric(origin) # At epoch
## 0
as.numeric(Sys.time()) # Right now (output as of July 21, 2016 at 11:47:37 EDT)
## 1469116057
posixlt = as.POSIXlt(Sys.time(), format ="%Y-%m-%d %H:%M:%S", tz = "America/Chicago")
# Conversion to POISXct
posixct = as.POSIXct(posixlt)
posixct
# Accessing components
posixlt$sec # Seconds 0-61
posixlt$min # Minutes 0-59
posixlt$hour # Hour 0-23
posixlt$mday # Day of the Month 1-31
posixlt$mon # Months after the first of the year 0-11
posixlt$year # Years since 1900.
ct = as.POSIXct("2015-05-25")
lt = as.POSIXlt("2015-05-25")
object.size(ct)
# 520 bytes
object.size(lt)
# 1816 bytes
Specialized packages
- anytime
- data.table IDate and ITime
- fasttime
- lubridate
- nanotime
