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)

_A_r_g_u_m_e_n_t_s:

       x: an object to be tested or coerced.

     ...: ignored.

_D_e_t_a_i_l_s:

     'is.null' is generic: you can write methods to handle specific
     classes of objects, see InternalMethods.

_R_e_f_e_r_e_n_c_e_s:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_. Wadsworth & Brooks/Cole.

_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'))

