# jacktest.r                 December 2007
 #
 # compare speeds for jackknife
 #
 # First method -- create matrix and use apply
 # data
  set.seed(5151917)
  N <- 1000
  v <- -log(runif(N))         # generate exponential RVs
  mean(v,trim=.2)             # compute statistic on data
 # 
  proc.time()       # read clock before execution
  V <- matrix(v,N-1,N)
 # compute statistic
  vps <- apply(V,2,mean,trim=.2)
  proc.time()       # read clock after execution
  var(vps)
  mean(vps)
 #
 # Second method -- using loop
  proc.time()       # read clock before execution
  vps <- rep(0,N)
  for(i in(1:N)){ vps[i]<-mean(v[-i],trim=.2) }
  proc.time()       # read clock after execution
  mean(vps)
  var(vps)
 # done
  rm(list=ls())
 q()