\Header{duplicated}{Determine Duplicate Elements}
\methalias{duplicated.data.frame}{duplicated}
\methalias{duplicated.default}{duplicated}
\keyword{logic}{duplicated}
\keyword{manip}{duplicated}
\begin{Description}\relax
Determines which elements of a vector of data frame are duplicates
of elements with smaller subscripts, and returns a logical vector
indicating which elements (rows) are duplicates.\end{Description}
\begin{Usage}
\begin{verbatim}
duplicated(x, incomparables = FALSE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] an atomic vector or a data frame.
\item[\code{incomparables}] a vector of values that cannot be compared.
Currently, \code{FALSE} is the only possible value, meaning that all
values can be compared.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
This is a generic function with methods for vectors and data frames.
The data frame method works by pasting together a character
representation of the rows separated by \code{\\r}, so may be imperfect
if the data frame has characters with embedded carriage returns or
columns which do not reliably map to characters.\end{Details}
\begin{SeeAlso}\relax
\code{\Link{unique}}.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
x <- c(9:20, 1:5, 3:7, 0:8)
## extract unique elements
(xu <- x[!duplicated(x)])
stopifnot(xu == unique(x), # but unique(x) is more efficient
          0:20 == sort(x[!duplicated(x)]))

data(iris)
stopifnot(duplicated(iris)[143] == TRUE)
\end{ExampleCode}
\end{Examples}

