interaction               package:base               R Documentation

_C_o_m_p_u_t_e _F_a_c_t_o_r _I_n_t_e_r_a_c_t_i_o_n_s

_D_e_s_c_r_i_p_t_i_o_n:

     'interaction' computes a factor which represents the interaction
     of the given factors.  The result of 'interaction' is always
     unordered.

_U_s_a_g_e:

     interaction(..., drop = FALSE, sep = ".")

_A_r_g_u_m_e_n_t_s:

     ...: the factors for which interaction is to be computed, or a
          single list giving those factors.

    drop: if 'drop' is 'TRUE', empty factor levels are dropped from the
          result.  The default is to retain all factor levels.

     sep: string to construct the new level labels by joining the
          constituent ones.

_V_a_l_u_e:

     A factor which represents the interaction of the given factors.
     The levels are labelled as the levels of the individual factors
     joined by 'sep', i.e. '.' by default.

_R_e_f_e_r_e_n_c_e_s:

     Chambers, J. M. and Hastie, T. J. (1992) _Statistical Models in
     S_. Wadsworth & Brooks/Cole.

_S_e_e _A_l_s_o:

     'factor'; ':' where 'f:g' is the same as 'interaction(f,g,
     sep=":")' when 'f' and  'g' are factors.

_E_x_a_m_p_l_e_s:

     a <- gl(2, 4, 8)
     b <- gl(2, 2, 8, label = c("ctrl", "treat"))
     s <- gl(2, 1, 8, label = c("M", "F"))
     interaction(a, b)
     interaction(a, b, s, sep = ":")

