update.formula             package:base             R Documentation

_M_o_d_e_l _U_p_d_a_t_i_n_g

_D_e_s_c_r_i_p_t_i_o_n:

     `update.formula' is used to update model formulae. This typically
     involves adding or dropping terms, but updates can be more
     general.

_U_s_a_g_e:

     update.formula(old, new)

_A_r_g_u_m_e_n_t_s:

     old: a model formula to be updated.

     new: a formula giving a template which specifies how to update.

_D_e_t_a_i_l_s:

     The function works by first identifying the left-hand side and
     right-hand side of the `old' formula. It then examines the `new'
     formula and substitutes the lhs of the `old' formula for any
     occurence of "`.'" on the left of `new', and substitutes the rhs
     of the `old' formula for any occurence of "`.'" on the right of
     `new'.

_V_a_l_u_e:

     The updated formula is returned.

_S_e_e _A_l_s_o:

     `terms', `model.matrix'.

