

_D_e_t_e_r_m_i_n_e _D_u_p_l_i_c_a_t_e _E_l_e_m_e_n_t_s

     duplicated(x)

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

     This function determines which elements of a vector are
     duplicates of elements with smaller subscripts, and
     returns a logical vector indicating which elements are
     duplicates.

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

     `unique'.

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

     x <- c(9:20, 1:5, 3:7, 0:8)
     # extract unique elements
     x[!duplicated(x)]
     all(0:20  == sort(x[!duplicated(x)]))

