interpprev               package:lgtdl               R Documentation

_I_n_t_e_r_p_o_l_a_t_i_o_n _U_s_i_n_g _t_h_e _P_r_e_v_i_o_u_s _V_a_l_u_e

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

     These functions provide an interpolation mechanism for objects of
     class 'lgtdl'. The 'AsIs' method is the vectorized version.

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

     interpprev(x, ...)
     interpprev.lgtdl(x, time, cov, ...)
     interpprev.AsIs(x, ...)

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

       x: 'x' is either an object of class 'lgtdl' or of class 'AsIs'.
          It is the object on which interpolation is to be performed.  

    time: A vector of times at which interpolation is requested.

     cov: The name of the covariate on which interpolation is
          requested. It is only required if 'x' has more than one
          covariate.

     ...: Ignored. 

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

     If objects of class 'lgtdl' are inserted into a data frame they
     become a vector with class 'AsIs'. In order to operate on these we
     provide a method for that class. The method is simply a vectorized
     version.

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

     'interpprev.lgtdl' returns a numeric vector of the interpolated
     values of the covariate at the time(s) specified by 'time'.
     'interpprev.AsIs' returns a vector of interpolated values of the
     covariate. In this case the vector contains one value for each
     element 'x'. 'time' must be either the same length as 'x' or of
     length one. In the latter case all interpolations are done at that
     time.

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

     Robert Gentleman

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

     'interplinear'

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

       x1<-data.frame(time=c(1,3,5), cov=c(4,6,8))
       x2<-data.frame(time=c(11,13,15), interest=c(66,45,88))
       x1<-as.lgtdl(x1)
       x2<-as.lgtdl(x2)
       interpprev(x1, c(2,4))
       interpprev(x2, c(12, 14))

