\Header{rank}{Sample Ranks}
\keyword{univar}{rank}
\begin{Description}\relax
Returns the sample ranks of the values in a numeric vector.
Ties, i.e., equal values, result in ranks being averaged, by default.
\end{Description}
\begin{Usage}
\begin{verbatim}
rank(x, na.last = TRUE, ties.method = c("average", "first", "random"))
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a numeric vector.
\item[\code{na.last}] for controlling the treatment of \code{\Link{NA}}s.
If \code{TRUE}, missing values in the data are put last; if
\code{FALSE}, they are put first; if \code{NA}, they are removed; if
\code{"keep"} they are kept.
\item[\code{ties.method}] a character string specifying how ties are treated,
see below; can be abbreviated.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
If all components are different, the ranks are well defined, with
values in \code{1:n} where \code{n <- length(x)} and we assume no
\code{NA}s for the moment.  Otherwise, with some values equal, called
\sQuote{ties}, the argument \code{ties.method} determines
the result at the corresponding indices.  The \code{"first"} method
results in a permutation with increasing values at each index set of
ties.  The \code{"random"} method puts these in random order whereas the
default, \code{"average"}, replaces them by their mean.
\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{\Link{order}} and \code{\Link{sort}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
(r1 <- rank(x1 <- c(3, 1, 4, 15, 92)))
x2 <- c(3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5)
names(x2) <- letters[1:11]
(r2 <- rank(x2)) # ties are averaged

## rank() is "idempotent": rank(rank(x)) == rank(x) :
stopifnot(rank(r1) == r1, rank(r2) == r2)

## ranks without averaging
rank(x2, ties.method= "first")  # first occurrence wins
rank(x2, ties.method= "random") # ties broken at random
rank(x2, ties.method= "random") # and again
\end{ExampleCode}
\end{Examples}

