\HeaderA{seq.POSIXt}{Generate Regular Sequences of Dates}{seq.POSIXt}
\keyword{manip}{seq.POSIXt}
\keyword{chron}{seq.POSIXt}
\begin{Description}\relax
The method for \code{\LinkA{seq}{seq}} for date-time classes.
\end{Description}
\begin{Usage}
\begin{verbatim}
## S3 method for class 'POSIXt':
seq(from, to, by, length.out = NULL, along.with = NULL, ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{from}] starting date. Required.
\item[\code{to}] end date. Optional.
\item[\code{by}] increment of the sequence. Optional. See Details.
\item[\code{length.out}] integer, optional. desired length of the sequence.
\item[\code{along.with}] take the length from the length of this argument.
\item[\code{...}] arguments passed to or from other methods.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
\code{by} can be specified in several ways.
\Itemize{
\item A number, taken to be in seconds.
\item A object of class \code{\LinkA{difftime}{difftime}}
\item A character string, containing one of \code{"sec"},
\code{"min"}, \code{"hour"}, \code{"day"}, \code{"DSTday"},
\code{"week"}, \code{"month"} 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 timezone of the result is taken from \code{from}: remember than
GMT 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.
\end{Details}
\begin{Value}
A vector of class \code{"POSIXct"}.
\end{Value}
\begin{SeeAlso}\relax
\code{\LinkA{DateTimeClasses}{DateTimeClasses}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
## first days of years
seq(ISOdate(1910,1,1), ISOdate(1999,1,1), "years")
## by month
seq(ISOdate(2000,1,1), by = "month", length = 12)
seq(ISOdate(2000,1,31), by = "month", length = 4)
## quarters
seq(ISOdate(1990,1,1), ISOdate(2000,1,1), by = "3 months")
## days vs DSTdays: use c() to lose the timezone.
seq(c(ISOdate(2000,3,20)), by = "day", length = 10)
seq(c(ISOdate(2000,3,20)), by = "DSTday", length = 10)
seq(c(ISOdate(2000,3,20)), by = "7 DSTdays", length = 4)
\end{ExampleCode}
\end{Examples}

