R/rtape_apply.R

In rtape: Manage and manipulate large collections of R objects stored as tape-like files

#' Iterate over tape, discarding results.
#' 
#' This function read the tape from the oldest to the newest writes and executes the callback function on each read object. Logically, it is an equivalent to \code{ignore<-lapply(rtapeAsList(fName),FUN,...)}, but it is optimized to store only the currently processed object in the memory and to discard \code{FUN} results as soon as they appear.
#'
#' @param fNames Name of the tape file to read; if this argument is a vector of several names, function behaves as reading a single tape made of all those tapes joined in a given order. 
#' @param FUN Callback function.
#' @param ... Additional parameters to \code{FUN}.
#' @author Miron B. Kursa \email{M.Kursa@@icm.edu.pl}
#' @examples
#' unlink('tmp.tape')
#' #Record something on the tape
#' rtapeAdd('tmp.tape',runif(3))
#' rtapeAdd('tmp.tape',rnorm(3))
#'
#' #Print tape contents
#' rtape_apply('tmp.tape',print)
#' unlink('tmp.tape')


rtape_apply<-function(fNames,FUN,...){
 FUN<-match.fun(FUN)
 for(fName in fNames){
  guessFileFormat(fName)(fName,open="rb")->con
  while(!.ckErr(try(unserialize(con),silent=TRUE)->x))
   FUN(x,...);
  close(con)
 }
 invisible(NULL)
}