NULL                  package: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())    # FALSE (on purpose!)
     is.null(integer(0))# F
     is.null(logical(0))# F
     as.null(list(a=1,b='c'))

