

_L_e_n_g_t_h _o_f _a _V_e_c_t_o_r _o_r _L_i_s_t

     length(x)
     length(x) <- n

_D_e_s_c_r_i_p_t_i_o_n:

     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.

_E_x_a_m_p_l_e_s:

     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

