\Header{NA}{Not Available / ``Missing'' Values}
\alias{is.na}{NA}
\alias{is.na.data.frame}{NA}
\keyword{NA}{NA}
\keyword{logic}{NA}
\keyword{manip}{NA}
\begin{Usage}
\begin{verbatim}
NA
is.na(x)
is.na.data.frame(x)
\end{verbatim}
\end{Usage}
\begin{Description}
\texttt{NA} is a logical constant of length 1 which contains
a missing value indicator.  \texttt{NA} can be freely coerced to any
other vector type.

The generic function \texttt{is.na} returns a logical vector
of the same ``form'' as its argument \texttt{x}, containing \texttt{TRUE}
for those elements marked \texttt{NA} or \texttt{\Link{NaN}} (!)
and \texttt{FALSE} otherwise.
\texttt{dim}, \texttt{dimnames} and \texttt{names} attributes are preserved.\end{Description}
\begin{Details}
\texttt{is.na(x)} works elementwise when \texttt{x} is a \texttt{\Link{list}}.

The method dispatching is C-internal, rather than via
\texttt{\Link{UseMethod}}.\end{Details}
\begin{SeeAlso}
\texttt{\Link{NaN}}, \texttt{\Link{is.nan}}, etc.
and the utility function \texttt{\Link{complete.cases}}.

\texttt{\Link{na.action}}, \texttt{\Link{na.omit}}, \texttt{\Link{na.fail}}
on how methods can be tuned to deal with missing values.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
is.na(c(1,NA))       #> F TRUE
is.na(paste(c(1,NA)))#> F FALSE

is.na(c(1,NA))       #> F TRUE
is.na(paste(c(1,NA)))#> F FALSE


\end{ExampleCode}
\end{Examples}

