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\name{chron}
\alias{chron}
\alias{as.chron}
\alias{as.chron.default}
\alias{as.chron.POSIXt}
\alias{as.chron.Date}
\alias{as.chron.factor}
\alias{is.chron}
\alias{as.data.frame.chron}
\alias{format.chron}
\alias{print.chron}
\title{
Create a Chronological Object
}
\description{
Create chrononogical objects which represent dates and times of day.
}
\usage{
chron(dates., times., format = c(dates = "m/d/y", times = "h:m:s"),
out.format, origin.)
}
\arguments{
\item{dates.}{character or numeric vector specifying dates. If
character, \code{dates.} are assumed to be in one of the date
formats below; if numeric, \code{dates.} are assumed to be Julian
dates, i.e., number of days since \code{origin.}.}
\item{times.}{optional character or numeric vector specifying times of
day. If character, \code{times.} are assumed to be in one of the
time formats below; if numeric, \code{times.} are assumed to be
fractions of a day.}
\item{format}{vector or list specifying the input format of the input.
The format can be either strings specifying one of the recognized
formats below or a list of user-supplied functions to convert dates
from character into Julian dates and vice versa.
The dates format can be any permutation of the characters
\code{"d"}, \code{"m"}, or \code{"y"} delimited by a separator
(possibly null), e.g., \code{"m/d/y"}, \code{"d-m-y"}, \code{"ymd"},
are all valid; the format can also be permutations of the words
\code{"day"}, \code{"month"} and \code{"year"} (with non-null
separator), which produces the month name, e.g., \code{"month day
year"} produces \code{"April 20 1992"}, \code{"day mon year"}
produces \code{"20 Apr 1992"}.
The times format can be any permutation of \code{"h"}, \code{"m"},
and \code{"s"} separated by any one non-special character. The
default is \code{"h:m:s"}.}
\item{out.format}{vector or list specifying date and time format for
printing and output. Default is same as \code{format}.}
\item{origin.}{a vector specifying the date with respect to which
Julian dates are computed. Default is
\code{c(month = 1, day = 1, year = 1970)};
you may set the option \code{chron.origin} to specify your own
default, e.g.,
\code{options(chron.origin = c(month=1, day=1, year=1990))}.}
}
\value{
An object of class \code{"times"} if only \code{times.} were
specified, \code{"dates"} if only \code{dates.}, or \code{"chron"} if
both \code{dates.} and \code{times.} were supplied. All these inherit
from class \code{"times"}.
These objects represent dates and times of day, and allow the
following arithmetic and summaries: subtraction \code{d1-d2},
constant addition \code{d1+constants}, all logical comparisons,
summaries \code{min()}, \code{max()}, and \code{range()} (which drop
NAs by default); constants specify days (fractions are converted to
time-of-day, e.g., 2.5 represents 2 days and 12 hours). Operations
such as sorting, differencing, etc., are automatically handled.
There are methods for \code{as.character()}, \code{as.numeric()},
\code{cut()}, \code{is.na()}, \code{print()}, \code{summary()},
\code{plot()}, \code{lines()}, \code{lag()}, and the usual subsetting
functions \code{[}, \code{[<-}.
The functions \code{days()}, \code{months()}, \code{quarters()},
\code{years()}, \code{weeks()}, \code{weekdays()}, \code{hours()},
\code{minutes()}, and \code{seconds()} take any \code{chron} object as
input and extract the corresponding time interval.
\code{cut()} is used to create ordered factors from \code{chron}
objects. Chronological objects may be used with the modeling software.
If \code{x} is \code{character} then it will be converted using
\code{as.POSIXct} (with the \code{format} argument, if any, passed to
\code{as.POSIXct}) and \code{tz = "GMT"} and then converted
to \code{chron}. If code{x} is \code{numeric} and \code{format}
is not specified then it will be converted to \code{chron}
using \code{chron(x)}. If code{x} is \code{numeric} and \code{format}
is \code{specified} then \code{x} will be converted to character and
then processed using \code{as.POSIXct} as discussed above. If the
format is specified as \code{NULL} it will be treated the same as if
it were \code{missing}.
The current implementation of \code{chron} objects does not handle
time zones nor daylight savings time.
}
\seealso{
\code{\link{dates}},
\code{\link{times}},
\code{\link{julian.default}},
\code{\link{cut.dates}},
\code{\link{seq.dates}}.
}
\examples{
dts <- dates(c("02/27/92", "02/27/92", "01/14/92",
"02/28/92", "02/01/92"))
dts
# [1] 02/27/92 02/27/92 01/14/92 02/28/92 02/01/92
tms <- times(c("23:03:20", "22:29:56", "01:03:30",
"18:21:03", "16:56:26"))
tms
# [1] 23:03:20 22:29:56 01:03:30 18:21:03 16:56:26
x <- chron(dates = dts, times = tms)
x
# [1] (02/27/92 23:03:19) (02/27/92 22:29:56) (01/14/92 01:03:30)
# [4] (02/28/92 18:21:03) (02/01/92 16:56:26)
# We can add or subtract scalars (representing days) to dates or
# chron objects:
c(dts[1], dts[1] + 10)
# [1] 02/27/92 03/08/92
dts[1] - 31
# [1] 01/27/92
# We can substract dates which results in a times object that
# represents days between the operands:
dts[1] - dts[3]
# Time in days:
# [1] 44
# Logical comparisons work as expected:
dts[dts > "01/25/92"]
# [1] 02/27/92 02/27/92 02/28/92 02/01/92
dts > dts[3]
# [1] TRUE TRUE FALSE TRUE TRUE
# Summary operations which are sensible are permitted and work as
# expected:
range(dts)
# [1] 01/14/92 02/28/92
diff(x)
# Time in days:
# [1] -0.02319444 -44.89335648 45.72052083 -27.05876157
sort(dts)[1:3]
# [1] 01/14/92 02/01/92 02/27/92
}
\keyword{chron}
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