unique                 package:base                 R Documentation

_E_x_t_r_a_c_t _U_n_i_q_u_e _E_l_e_m_e_n_t_s

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

     'unique' returns a vector, data frame or array like 'x' but with
     duplicate  elements removed.

_U_s_a_g_e:

     unique(x, incomparables = FALSE, ...)

     ## S3 method for class 'array':
     unique(x, incomparables = FALSE, MARGIN = 1, ...)

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

       x: a vector or a data frame or an array or 'NULL'.

incomparables: a vector of values that cannot be compared. Currently,
          'FALSE' is the only possible value, meaning that all values
          can be compared.

     ...: arguments for particular methods.

  MARGIN: the array margin to be held fixed: a single integer.

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

     This is a generic function with methods for vectors, data frames
     and arrays (including matrices).

     The array method calculates for each element of the dimension
     specified by 'MARGIN' if the remaining dimensions are identical to
     those for an earlier element (in row-major order).  This would
     most commonly be used to find unique rows (the default) or columns
     (with 'MARGIN = 2').

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

     An object of the same type of 'x'. but if an element is equal to
     one with a smaller index, it is removed. Dimensions of arrays are
     not dropped.

_W_a_r_n_i_n_g:

     Using this for lists is potentially slow, especially if the
     elements are not atomic vectors (see 'vector') or differ only in
     their attributes.  In the worst case it is O(n^2).

_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.

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

     'duplicated' which gives the indices of duplicated elements.

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

     unique(c(3:5, 11:8, 8 + 0:5))
     length(unique(sample(100, 100, replace=TRUE)))
     ## approximately 100(1 - 1/e) = 63.21

     unique(iris)

