

   NNuummeerriicc VVeeccttoorrss

        numeric(length = 0)
        as.numeric(x)
        is.numeric(x)

   DDeessccrriippttiioonn::

        `numeric' creates a real vector of the specified
        length.  The elements of the vector are all equal to
        `0'.

        `as.numeric' attempts to coerce its argument to numeric
        type (either integer or real).

        `is.numeric' returns `TRUE' if its argument is of type
        real or type integer and `FALSE' otherwise.

   NNoottee::

        R has no single precision data type.  All real numbers
        are stored in double precision format.

        `as.numeric' for factors yields the codes underlying
        the factor levels.

   EExxaammpplleess::

        as.numeric(c("2","B"))
        as.numeric(factor(5:10))

