\Header{sample}{Random Samples and Permutations}
\keyword{distribution}{sample}
\begin{Description}\relax
\code{sample} takes a sample of the specified size from
the elements of \code{x} using either with or without replacement.\end{Description}
\begin{Usage}
\begin{verbatim}
sample(x, size, replace = FALSE, prob = NULL)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] Either a (numeric, complex, character or logical)
vector of more than one element from which to
choose, or a positive integer.
\item[\code{size}] A positive integer giving the number of items to choose.
\item[\code{replace}] Should sampling be with replacement?
\item[\code{prob}] A vector of probability weights for obtaining the elements
of the vector being sampled.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
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.\end{Details}
\begin{Examples}
\begin{ExampleCode}
x <- 1:12
# a random permutation
sample(x)
# bootstrap sampling
sample(x,replace=TRUE)

# 100 Bernoulli trials
sample(c(0,1), 100, replace = TRUE)
\end{ExampleCode}
\end{Examples}

