

   LLeennggtthh ooff aa VVeeccttoorr oorr LLiisstt

        length(x)
        length(x) <- n

   DDeessccrriippttiioonn::

        If `x' is (or can be coerced to) a vector or list,
        `length' returns the length of `x'.  Otherwise,
        `length' returns `NA'.

        The second form above can be used to reset the length
        of a vector.  If a vector is shortened, extra values
        are discarded and when a vector is lengthened, it is
        padded out to its new length with `NA's.

   EExxaammpplleess::

        length(diag(4))# = 16 (4 x 4)
        length(options())# 12 or more..
        length(y ~ x1 + x2 + x3)# 3
        length(expression(x, {y <- x^2; y+2}, x^y)) # 3

