Date and time classes with integer storage for fast sorting and
grouping. Still experimental!
Usage
as.IDate(x, ...)
## Default S3 method:
as.IDate(x, ...)
## S3 method for class 'Date'
as.IDate(x, ...)
## S3 method for class 'IDate'
as.Date(x, ...)
## S3 method for class 'IDate'
as.POSIXct(x, tz = "UTC", time = 0, ...)
## S3 method for class 'IDate'
as.chron(x, time = NULL, ...)
## S3 method for class 'IDate'
round(x, digits = c("weeks", "months", "quarters","years"), ...)
as.ITime(x, ...)
## Default S3 method:
as.ITime(x, ...)
## S3 method for class 'ITime'
as.POSIXct(x, tz = "UTC", date = as.Date(Sys.time()), ...)
## S3 method for class 'ITime'
as.chron(x, date = NULL, ...)
## S3 method for class 'ITime'
as.character(x, ...)
## S3 method for class 'ITime'
format(x, ...)
IDateTime(x, ...)
## Default S3 method:
IDateTime(x, ...)
hour(x)
yday(x)
wday(x)
mday(x)
week(x)
month(x)
quarter(x)
year(x)
Arguments
x
an object
...
arguments to be passed to or from other methods. For
as.IDate.default, arguments are passed to as.Date. For
as.ITime.default, arguments are passed to as.POSIXlt.
tz
time zone (see strptime).
date
date object convertable with as.IDate.
time
time-of-day object convertable with as.ITime.
digits
really units; one of the units listed for rounding. May be abbreviated.
Details
IDate is a date class derived from Date. It has the same
internal representation as the Date class, except the storage
mode is integer. IDate is a relatively simple wrapper, and it
should work in almost all situations as a replacement for Date.
Functions that use Date objects generally work for
IDate objects. This package provides specific methods for
IDate objects for mean, cut, seq, c,
rep, and split to return an IDate object.
ITime is a time-of-day class stored as the integer number of
seconds in the day. as.ITime does not allow days longer than 24
hours. Because ITime is stored in seconds, you can add it to a
POSIXct object, but you should not add it to a Date
object.
Conversions to and from Date, POSIXct, and chron
formats are provided.
ITime does not account for time zones. When converting
ITime and IDate to POSIXct with as.POSIXct, a time
zone may be specified.
In as.POSIXct methods for ITime and IDate, the
second argument is required to be tz based on the generic
template, but to make converting easier, the second arguement is
interpreted as a date instead of a time zone if it is of type
IDate or ITime. Therefore, you can use either of the
following: as.POSIXct(time, date) or as.POSIXct(date,
time).
IDateTime takes a date-time input and returns a data table with
columns date and time.
Using integer storage allows dates and/or times to be used as data table
keys. With positive integers with a range less than 100,000, grouping
and sorting is fast because radix sorting can be used (see
sort.list).
Several convenience functions like hour and quarter are
provided to group or extract by hour, month, and other date-time
intervals. as.POSIXlt is also useful. For example,
as.POSIXlt(x)$mon is the integer month. The R base convenience
functions weekdays, months, and quarters can also
be used, but these return character values, so they must be converted to
factors for use with data.table.
The round method for IDate's is useful for grouping and plotting. It can
round to weeks, months, quarters, and years.
Value
For as.IDate, a class of IDate and Date with the
date stored as the number of days since some origin.
For as.ITime, a class of ITime
stored as the number of seconds in the day.
For IDateTime, a data table with columns idate and
itime in IDate and ITime format.
hour, codeyday, wday, mday, week,
month, quarter, and year return integer values
for hour, day of year, day of week, day of month, week, month,
quarter, and year.
Author(s)
Tom Short, t.short@ieee.org
References
G. Grothendieck and T. Petzoldt, “Date and Time Classes in R,”
R News, vol. 4, no. 1, June 2004.
H. Wickham, http://gist.github.com/10238.
See Also
as.Date, as.POSIXct,
strptime, DateTimeClasses
Examples
# create IDate:
(d <- as.IDate("2001-01-01"))
# S4 coercion also works
identical(as.IDate("2001-01-01"), as("2001-01-01", "IDate"))
# create ITime:
(t <- as.ITime("10:45"))
# S4 coercion also works
identical(as.ITime("10:45"), as("10:45", "ITime"))
(t <- as.ITime("10:45:04"))
(t <- as.ITime("10:45:04", format = "%H:%M:%S"))
as.POSIXct("2001-01-01") + as.ITime("10:45")
datetime <- seq(as.POSIXct("2001-01-01"), as.POSIXct("2001-01-03"), by = "5 hour")
(af <- data.table(IDateTime(datetime), a = rep(1:2, 5), key = "a,idate,itime"))
af[, mean(a), by = "itime"]
af[, mean(a), by = list(hour = hour(itime))]
af[, mean(a), by = list(wday = factor(weekdays(idate)))]
af[, mean(a), by = list(wday = wday(idate))]
as.POSIXct(af$idate)
as.POSIXct(af$idate, time = af$itime)
as.POSIXct(af$idate, af$itime)
as.POSIXct(af$idate, time = af$itime, tz = "GMT")
as.POSIXct(af$itime, af$idate)
as.POSIXct(af$itime) # uses today's date
(seqdates <- seq(as.IDate("2001-01-01"), as.IDate("2001-08-03"), by = "3 weeks"))
round(seqdates, "months")
if (require(chron)) {
as.chron(as.IDate("2000-01-01"))
as.chron(as.ITime("10:45"))
as.chron(as.IDate("2000-01-01"), as.ITime("10:45"))
as.chron(as.ITime("10:45"), as.IDate("2000-01-01"))
as.ITime(chron(times = "11:01:01"))
IDateTime(chron("12/31/98","10:45:00"))
}