Here comes yet another sequel of the code optimization problem from the R wiki, still using Rcpp, but with a different strategy this time

Essentially, my previous version (15) was using stringstream although we don't really need its functionality and it was slowing us down

Also, the characters "i" and "." are always on the same position so we can assign them once and for all

So without further ado, here is attempt 17:

With quite a speedup from attempt 15:

                test replications elapsed relative
2 generateIndex17(n)           20   9.363 1.000000
1 generateIndex15(n)           20  17.795 1.900566