

_S_e_t_s _C_o_n_t_r_a_s_t_s _f_o_r _a _F_a_c_t_o_r

     C(object, contr, how.many)

_A_r_g_u_m_e_n_t_s:

  object: a factor or ordered factor

   contr: which contrasts to use. Can be a matrix with one
          row for each level of the factor or a suitable
          function like `contr.poly' or a character string
          giving the name of the function

how.many: the number of contrasts to set, by default one
          less than `nlevels(object)'.

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

     Sets the `"contrasts"' attribute for the factor.

_D_e_t_a_i_l_s:

     For compatibility with S, `contr' can be `treatment',
     `helmert', `sum' or `poly' (without quotes) as short-
     hand for `contr.treatment' and so on.

_V_a_l_u_e:

     The factor with the  `"contrasts"' attribute set.

_A_u_t_h_o_r(_s):

     B.D. Ripley

_S_e_e _A_l_s_o:

     `contrasts'

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

     data(warpbreaks)
     attach(warpbreaks)
     tens <- C(tension, poly, 1)
     attributes(tens)
     detach()
     ## tension SHOULD be an ordered factor, but as it is not we can use
     aov(breaks ~ wool + tens + tension, data=warpbreaks)

     data(esoph) # following on from help(esoph)
     model3 <- glm(cbind(ncases, ncontrols) ~ agegp + C(tobgp,, 1) +
          C(alcgp,, 1), data = esoph, family = binomial())
     summary(model3)

