R version 3.1.2 beta (2014-10-21 r66834) -- "Pumpkin Helmet"
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> #### These are *NOT* compared with output in the released version of
> ###  'cluster'  currently
> 
> library(cluster)
> 
> data(xclara)
> ## Try 100 times *different* random samples -- for reliability:
> nSim <- 100
> nCl <- 3 # = no.classes
> ## unknown problem: this is still platform dependent to some extent:
> 
> set.seed(107)# (reproducibility; somewhat favorable with "small iDoubt")
> cl <- replicate(nSim, clara(xclara, nCl, rngR = TRUE)$cluster)
> tcl <- apply(cl,1, tabulate, nbins = nCl)
> ## those that are not always in same cluster (5 out of 3000 for this seed):
> (iDoubt <- which(apply(tcl,2, function(n) all(n < nSim))))
 [1]    6   71  243  245  610  708  727  770 1038 1081 1120 1248 1289 1610 1644
[16] 1922
> 
> if(FALSE) {# doExtras --
+ rrr <- lapply(1:128, function(iseed) {
+     set.seed(iseed)# (reproducibility; somewhat favorable with "small iDoubt")
+     cat(iseed, if(iseed %% 10 == 0)"\n")
+     cl <- replicate(nSim, clara(xclara, nCl, rngR = TRUE)$cluster)
+     tcl <- apply(cl,1, tabulate, nbins = nCl)
+     which(apply(tcl,2, function(n) all(n < nSim)))
+ })
+ ## compare with "true" -- are the "changers" only those with small sil.width?
+ 
+ print(system.time(px <- pam(xclara,3)))# 1.84 on lynne(2013)
+ }## doExtras
> 
> 
> if(length(iDoubt)) { # (not for all seeds)
+   tabD <- tcl[,iDoubt, drop=FALSE]
+   dimnames(tabD) <- list(cluster = paste(1:nCl), obs = format(iDoubt))
+   t(tabD) # how many times in which clusters
+ }
      cluster
obs     1  2  3
     6 98  2  0
    71 99  1  0
   243 98  0  2
   245 86  0 14
   610 84 16  0
   708 87 13  0
   727 87  0 13
   770  0  1 99
  1038 80 20  0
  1081 48 52  0
  1120  5 95  0
  1248 21 79  0
  1289  3 97  0
  1610 59 41  0
  1644 18 82  0
  1922 10 90  0
> 
> proc.time()
   user  system elapsed 
  0.408   0.016   0.479