\HeaderA{ts}{Time-Series Objects}{ts}
\aliasA{as.ts}{ts}{as.ts}
\methaliasA{as.ts.default}{ts}{as.ts.default}
\aliasA{cbind.ts}{ts}{cbind.ts}
\aliasA{is.mts}{ts}{is.mts}
\aliasA{is.ts}{ts}{is.ts}
\aliasA{Ops.ts}{ts}{Ops.ts}
\aliasA{t.ts}{ts}{t.ts}
\aliasA{[.ts}{ts}{[.ts}
\keyword{ts}{ts}
\begin{Description}\relax
The function \code{ts} is used to create time-series objects.

\code{as.ts} and \code{is.ts} coerce an object to a time-series and
test whether an object is a time series.
\end{Description}
\begin{Usage}
\begin{verbatim}
ts(data = NA, start = 1, end = numeric(0), frequency = 1,
   deltat = 1, ts.eps = getOption("ts.eps"), class = , names = )
as.ts(x, ...)
is.ts(x)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{data}] a numeric vector or matrix of the observed time-series
values. A data frame will be coerced to a numeric matrix via
\code{data.matrix}.
\item[\code{start}] the time of the first observation.  Either a single
number or a vector of two integers, which specify a natural time
unit and a (1-based) number of samples into the time unit.  See
the examples for the use of the second form.
\item[\code{end}] the time of the last observation, specified in the same way
as \code{start}.
\item[\code{frequency}] the number of observations per unit of time.
\item[\code{deltat}] the fraction of the sampling period between successive
observations; e.g., 1/12 for monthly data.  Only one of
\code{frequency} or \code{deltat} should be provided.
\item[\code{ts.eps}] time series comparison tolerance.  Frequencies are
considered equal if their absolute difference is less than
\code{ts.eps}.
\item[\code{class}] class to be given to the result, or none if \code{NULL}
or \code{"none"}.  The default is \code{"ts"} for a single series,
\code{c("mts", "ts")} for multiple series.
\item[\code{names}] a character vector of names for the series in a multiple
series: defaults to the colnames of \code{data}, or \code{Series 1},
\code{Series 2}, \dots.
\item[\code{x}] an arbitrary \R{} object.
\item[\code{...}] arguments passed to methods (unused for the default method).
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The function \code{ts} is used to create time-series objects.  These
are vector or matrices with class of \code{"ts"} (and additional
attributes) which represent data which has been sampled at equispaced
points in time.  In the matrix case, each column of the matrix
\code{data} is assumed to contain a single (univariate) time series.
Time series must have at least one observation, and although they need
not be numeric there is very limited support for non-numeric series.

Class \code{"ts"} has a number of methods.  In particular arithmetic
will attempt to align time axes, and subsetting to extract subsets of
series can be used (e.g., \code{EuStockMarkets[, "DAX"]}).  However,
subsetting the first (or only) dimension will return a matrix or
vector, as will matrix subsetting.  Subassignment can be used to
replace values but not to extend a series (see \code{\LinkA{window}{window}}).
There is a method for \code{\LinkA{t}{t}} that transposes the series as a
matrix (a one-column matrix if a vector) and hence returns a result
that does not inherit from class \code{"ts"}.

The value of argument \code{frequency} is used when the series is
sampled an integral number of times in each unit time interval.  For
example, one could use a value of \code{7} for \code{frequency} when
the data are sampled daily, and the natural time period is a week, or
\code{12} when the data are sampled monthly and the natural time
period is a year.  Values of \code{4} and \code{12} are assumed in
(e.g.) \code{print} methods to imply a quarterly and monthly series
respectively.

\code{as.ts} is generic.  Its default method will use the
\code{\LinkA{tsp}{tsp}} attribute of the object if it has one to set the
start and end times and frequency.

\code{is.ts} tests if an object is a time series.  It is generic: you
can write methods to handle specific classes of objects,
see \LinkA{InternalMethods}{InternalMethods}.
\end{Details}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{tsp}{tsp}},
\code{\LinkA{frequency}{frequency}},
\code{\LinkA{start}{start}},
\code{\LinkA{end}{end}},
\code{\LinkA{time}{time}},
\code{\LinkA{window}{window}};
\code{\LinkA{print.ts}{print.ts}}, the print method for time series objects;
\code{\LinkA{plot.ts}{plot.ts}}, the plot method for time series objects.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
require(graphics)

ts(1:10, frequency = 4, start = c(1959, 2)) # 2nd Quarter of 1959
print( ts(1:10, frequency = 7, start = c(12, 2)), calendar = TRUE)
# print.ts(.)
## Using July 1954 as start date:
gnp <- ts(cumsum(1 + round(rnorm(100), 2)),
          start = c(1954, 7), frequency = 12)
plot(gnp) # using 'plot.ts' for time-series plot

## Multivariate
z <- ts(matrix(rnorm(300), 100, 3), start=c(1961, 1), frequency=12)
class(z)
plot(z)
plot(z, plot.type="single", lty=1:3)

## A phase plot:
plot(nhtemp, c(nhtemp[-1], NA), cex = .8, col="blue",
     main = "Lag plot of New Haven temperatures")
## a clearer way to do this would be
## Not run: 
plot(nhtemp, lag(nhtemp, 1), cex = .8, col="blue",
     main = "Lag plot of New Haven temperatures")
## End(Not run)\end{ExampleCode}
\end{Examples}

