date.object             package:survival             R Documentation

_D_a_t_e _O_b_j_e_c_t_s

_D_e_s_c_r_i_p_t_i_o_n:

     Objects of class '"date"'.

_U_s_a_g_e:

     is.date(x)

_A_r_g_u_m_e_n_t_s:

       x: any R object.

_D_e_t_a_i_l_s:

     Dates are stored as the number of days since 1/1/1960, and are
     kept in integer format.  (This is the same baseline value as is
     used by SAS).  The numerical methods for dates treat 'date - date'
     as a numeric, and 'date +- numeric' as a date.

     'is.date' returns 'TRUE' if 'x' has class '"date"', and 'FALSE'
     otherwise.  Its behavior is unaffected by any attributes of 'x';
     for example, 'x' could be a date array (in contrast to the
     behavior of 'is.vector').

     'as.date' returns 'x' if 'x' is a simple object of class '"date"',
     and otherwise a date vector of the same length as 'x' and with
     data resulting from coercing the elements of 'x' to class
     '"date"'.  See the manual page for 'as.date()' for details.

     Logical operations as well as the numeric functions 'exp()',
     'log()', and so on are invalid.

     Other methods exist for missing value, 'as.character()', printing,
     and summarizing.

_S_e_e _A_l_s_o:

     'date.mdy', 'mdy.date', 'date.ddmmmyy',  'as.date'.