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% $Id: combinations.Rd 1433 2010-05-01 22:03:03Z warnes $
%
\name{combinations}
\alias{combinations}
\alias{permutations}
\title{Enumerate the Combinations or Permutations of the Elements of a Vector}
\description{
\code{combinations} enumerates the possible combinations of a
specified size from the elements of a vector. \code{permutations}
enumerates the possible permutations.
}
\usage{
combinations(n, r, v=1:n, set=TRUE, repeats.allowed=FALSE)
permutations(n, r, v=1:n, set=TRUE, repeats.allowed=FALSE)
}
%- maybe also `usage' for other objects documented here.
\arguments{
\item{n}{ Size of the source vector }
\item{r}{ Size of the target vectors }
\item{v}{ Source vector. Defaults to \code{1:n}}
\item{set}{ Logical flag indicating whether duplicates should be
removed from the source vector \code{v}. Defaults to \code{TRUE}.}
\item{repeats.allowed}{ Logical flag indicating whether the
constructed vectors may include duplicated values. Defaults to
\code{FALSE}. }
}
\details{
Caution: The number of combinations and permutations increases rapidly
with \code{n} and \code{r}!.
To use values of \code{n} above about 45, you will need to increase
R's recursion limit. See the \code{expression} argument to the
\code{options} command for details on how to do this.
}
\value{
Returns a matrix where each row contains a vector of length \code{r}.
}
\references{Venables, Bill. "Programmers Note", R-News, Vol 1/1,
Jan. 2001. \url{http://cran.r-project.org/doc/Rnews} }
\author{ Original versions by Bill Venables
\email{Bill.Venables@cmis.csiro.au}. Extended to handle
\code{repeats.allowed} by Gregory R. Warnes
\email{greg@warnes.net}.
}
\seealso{ \code{\link[base]{choose}}, \code{\link[base]{options}} }
\examples{
combinations(3,2,letters[1:3])
combinations(3,2,letters[1:3],repeats=TRUE)
permutations(3,2,letters[1:3])
permutations(3,2,letters[1:3],repeats=TRUE)
# To use large 'n', you need to change the default recusion limit
options(expressions=1e5)
cmat <- combinations(300,2)
dim(cmat) # 44850 by 2
}
\keyword{ manip }
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