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 'matrix':
     unique(x, incomparables = FALSE, MARGIN = 1, ...)

     ## 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 for matrices to find unique rows (the
     default) or columns (with 'MARGIN = 2').

_V_a_l_u_e:

     For a vector, an object of the same type of 'x', but with only one
     copy of each duplicated element.  No attributes are copied (so the
     result has no names).

     For a data frame, a data frame is returned with the same columns
     but possibly fewer rows (and with row names from the first
     occurrences of the unique rows).

     A matrix or array is subsetted by '[, drop = FALSE]', so
     dimensions and dimnames are copied appropriately, and the result
     always has the same number of dimensions as 'x'.

_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)

