The R Project SVN R

\name{sample}
\title{Random Samples and Permutations}
\usage{
sample(x, size, replace=FALSE, prob)
}
\alias{sample}
\arguments{
  \item{x}{Either a (numeric, complex, character or logical)
    vector of more than one element from which to
    choose, or a positive integer.}
  \item{size}{A positive integer giving the number of items to choose.}
  \item{replace}{Should sampling be with replacement?}
  \item{prob}{A vector of probability weights for obtaining the elements
    of the vector being sampled.}
}
\description{
  \code{sample} takes a sample of the specified size from
  the elements of \code{x} using either with or without replacement.
}
\details{
  If \code{x} has length 1, sampling takes place from
  \code{1:x}.

  By default \code{size} is equal to \code{length(x)}
  so that \code{sample(x)} generates a random permutation
  of the elements of \code{x} (or \code{1:x}).
  
  The optional \code{prob} argument can be used to give a vector
  of weights for obtaining the elements of the vector being
  sampled. They need not sum to one, but they should be nonnegative
  and not all zero. 
  If \code{replace} is false, these probabilities are applied
  sequentially, that is the probability of choosing the next item is
  proportional to the probabilities amongst the remaining items. The number
  of nonzero weights must be at least \code{size} in this case.
}
\examples{
x <- 1:12
# a random permutation
sample(x)
# bootstrap sampling
sample(x,replace=TRUE)

# 100 Bernoulli trials
sample(c(0,1), 100, replace = TRUE)
}
\keyword{distribution}