

   CCoolluummnn IInnddeexxeess

        col(x, as.factor=FALSE)

   AArrgguummeennttss::

          x: a matrix.

   as.factor: a logical value indicating whether the value
             should be returned as a factor rather than as
             numeric.

   VVaalluuee::

        An integer matrix with the same dimensions as `x' and
        whose `ij'-th element is equal to `j'.

   SSeeee AAllssoo::

        `row' to get rows.

   EExxaammpplleess::

        # 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

