\HeaderA{c}{Combine Values into a Vector or List}{c}
\keyword{manip}{c}
\begin{Description}\relax
This is a generic function which combines its arguments.

The default method combines its arguments to form a vector.
All arguments are coerced to a common type which is the type
of the returned value, and all attributes except names are removed.
\end{Description}
\begin{Usage}
\begin{verbatim}
c(..., recursive=FALSE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{...}] objects to be concatenated.
\item[\code{recursive}] logical.  If \code{recursive = TRUE}, the function
recursively descends through lists (and pairlists) combining all
their elements into a vector.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The output type is determined from the highest type of the components
in the hierarchy NULL < raw < logical < integer < real < complex < character
< list < expression.  Pairlists are treated as lists, but non-vector
components (such names and calls) are treated as one-element lists
which cannot be unlisted even if \code{recursive = TRUE}.

\code{c} is sometimes used for its side effect of removing attributes
except names, for example to turn an array into a vector.
\code{as.vector} is a more intuitive way to do this, but also drops
names.  Note too that methods other than the default are not required
to do this (and they will almost certainly preserve a class attribute).
\end{Details}
\begin{Value}
\code{NULL} or an expression or a vector of an appropriate mode.
(With no arguments the value is \code{NULL}.)
\end{Value}
\begin{Section}{S4 methods}
This function is S4 generic, but with argument list
\code{(x, ..., recursive = FALSE)}.
\end{Section}
\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{unlist}{unlist}} and \code{\LinkA{as.vector}{as.vector}} to produce
attribute-free vectors.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
c(1,7:9)
c(1:5, 10.5, "next")

## uses with a single argument to drop attributes
x <- 1:4
names(x) <- letters[1:4]
x
c(x)          # has names
as.vector(x)  # no names
dim(x) <- c(2,2)
x
c(x)
as.vector(x)

## append to a list:
ll <- list(A = 1, c="C")
## do *not* use
c(ll, d = 1:3) # which is == c(ll, as.list(c(d=1:3))
## but rather
c(ll, d = list(1:3))# c() combining two lists

c(list(A=c(B=1)), recursive=TRUE)

c(options(), recursive=TRUE)
c(list(A=c(B=1,C=2), B=c(E=7)), recursive=TRUE)
\end{ExampleCode}
\end{Examples}

