\Header{col}{Column Indexes}
\keyword{array}{col}
\begin{Description}\relax
Returns a matrix of integers indicating their column number in the
matrix.\end{Description}
\begin{Usage}
\begin{verbatim}
col(x, as.factor=FALSE)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a matrix.
\item[\code{as.factor}] a logical value indicating whether the value should
be returned as a factor rather than as numeric.
\end{ldescription}
\end{Arguments}
\begin{Value}
An integer matrix with the same dimensions as \code{x} and whose
\code{ij}-th element is equal to \code{j}.\end{Value}
\begin{SeeAlso}\relax
\code{\Link{row}} to get rows.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
# extract an off-diagonal of a matrix
ma <- matrix(1:12, 3, 4)
ma[row(ma) == col(ma) + 1]

# create an identity 5-by-5 matrix
x <- matrix(0, nr = 5, nc = 5)
x[row(x) == col(x)] <- 1
\end{ExampleCode}
\end{Examples}

