boot.array               package:boot               R Documentation

Bootstrap Resampling Arrays

Description:

     This function takes a bootstrap object calculated by one of the
     functions 'boot', 'censboot', or 'tilt.boot' and returns the
     frequency (or index) array for the the bootstrap resamples.

Usage:

     boot.array(boot.out, indices=)

Arguments:

boot.out: An object of class '"boot"' returned by one of the generation
          functions for such an object. 

 indices: A logical argument which specifies whether to return the
          frequency array or the raw index array.  The default is
          'indices=FALSE' unless 'boot.out' was created by 'tsboot' in
          which case the default is 'indices=TRUE'. 

Details:

     The process by which the original index array was generated is
     repeated with the same value of '.Random.seed'.  If the frequency
     array is required then 'freq.array' is called to convert the index
     array to a frequency array.

     A resampling array can only be returned when such a concept makes
     sense.  In particular it cannot be found for any parametric or
     model-based resampling schemes.  Hence for objects generated by
     'censboot' the only resampling scheme for which such an array can
     be found is ordinary case resampling. Similarly if 'boot.out$sim'
     is '"parametric"' in the case of 'boot' or '"model"' in the case
     of 'tsboot' the array cannot be found.  Note also that for
     post-blackened bootstraps from 'tsboot' the indices found will
     relate to those prior to any post-blackening and so will not be
     useful.

     Frequency arrays are used in many post-bootstrap calculations such
     as the jackknife-after-bootstrap and finding importance sampling
     weights. They are also used to find empirical influence values
     through the regression method.

Value:

     A matrix with 'boot.out$R' rows and 'n' columns where 'n' is the
     number of observations in 'boot.out$data'.  If 'indices' is
     'FALSE' then this will give the frequency of each of the original
     observations in each bootstrap resample. If 'indices' is 'TRUE' it
     will give the indices of the bootstrap resamples in the order in
     which they would have been passed to the statistic.

Side Effects:

     This function temporarily resets '.Random.seed' to the value in
     'boot.out$seed' and then returns it to its original value at the
     end of the function.

See Also:

     'boot', 'censboot', 'freq.array', 'tilt.boot', 'tsboot'

Examples:

     #  A frequency array for a nonparametric bootstrap
     city.boot <- boot(city, corr, R=40, stype="w")
     boot.array(city.boot)

     perm.cor <- function(d,i) 
          cor(d$x,d$u[i])
     city.perm <- boot(city, perm.cor, R=40, sim="permutation")
     boot.array(city.perm, indices=TRUE)

