The R Project SVN R

% File src/library/base/man/seq.POSIXt.Rd

% Part of the R package, https://www.R-project.org

% Copyright 1995-2017 R Core Team

% Distributed under GPL 2 or later

\name{seq.POSIXt}

\alias{seq.POSIXt}

\title{Generate Regular Sequences of Times}

\description{

  The method for \code{\link{seq}} for date-time classes.

}

\usage{

\method{seq}{POSIXt}(from, to, by, length.out = NULL, along.with = NULL, \dots)

}

\arguments{

  \item{from}{starting date.  Required.}

  \item{to}{end date.  Optional.}

  \item{by}{increment of the sequence.  Optional.  See \sQuote{Details}.}

  \item{length.out}{integer, optional.  Desired length of the sequence.}

  \item{along.with}{take the length from the length of this argument.}

  \item{\dots}{arguments passed to or from other methods.}

}

\details{

  \code{by} can be specified in several ways.

  \itemize{

    \item A number, taken to be in seconds.

    \item A object of class \code{\link{difftime}}

    \item A character string, containing one of \code{"sec"},

    \code{"min"}, \code{"hour"}, \code{"day"}, \code{"DSTday"},

    \code{"week"}, \code{"month"}, \code{"quarter"} or \code{"year"}.

    This can optionally be preceded by a (positive or negative) integer

    and a space, or followed by \code{"s"}.

  }

  The difference between \code{"day"} and \code{"DSTday"} is that the

  former ignores changes to/from daylight savings time and the latter takes

  the same clock time each day.  \code{"week"} ignores DST (it is a

  period of 144 hours), but \code{"7 DSTdays"} can be used as an

  alternative.  \code{"month"} and \code{"year"} allow for DST.

  The \link{time zone} of the result is taken from \code{from}: remember

  that GMT means UTC (and not the time zone of Greenwich, England) and so

  does not have daylight savings time.

  Using \code{"month"} first advances the month without changing the

  day: if this results in an invalid day of the month, it is counted

  forward into the next month: see the examples.

}

\value{

  A vector of class \code{"POSIXct"}.

}

\seealso{\code{\link{DateTimeClasses}}}

\examples{

## first days of years

seq(ISOdate(1910,1,1), ISOdate(1999,1,1), "years")

## by month

seq(ISOdate(2000,1,1), by = "month", length.out = 12)

seq(ISOdate(2000,1,31), by = "month", length.out = 4)

## quarters

seq(ISOdate(1990,1,1), ISOdate(2000,1,1), by = "quarter") # or "3 months"

## days vs DSTdays: use c() to lose the time zone.

seq(c(ISOdate(2000,3,20)), by = "day", length.out = 10)

seq(c(ISOdate(2000,3,20)), by = "DSTday", length.out = 10)

seq(c(ISOdate(2000,3,20)), by = "7 DSTdays", length.out = 4)

}

\keyword{manip}

\keyword{chron}