

NULL {base}                                  R Documentation

_T_h_e _N_u_l_l _O_b_j_e_c_t

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

     `NULL' represents the null object in R.  NULL is used
     mainly to represent the lists with zero length, and is
     often returned by expressions and functions whose value
     is undefined.

     `as.null' ignores its argument and returns the value
     `NULL'.

     `is.null' returns `TRUE' if its argument is `NULL' and
     `FALSE' otherwise.

_U_s_a_g_e_:

     NULL
     as.null(x)
     is.null(x)

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

     is.null(list())    # TRUE (not so in S)
     is.null(integer(0))# F
     is.null(logical(0))# F
     as.null(list(a=1,b='c'))

