# /* vim: set filetype=awk : */ -*- awk -*-

BEGIN  { 
  Trainf = "train.arff"; 
  Testf  = "test.arff"; 
  Seed   = 1;
  Bins   = 3; 
  Bin    = 1; 
} 
                    { sub(/%.*/,"") }
/^[ \t]*$/          { next }
/@relation/         { srand(Seed ? Seed : 1);     
                      printf "">Trainf;  
                      printf "">Testf 
                    }
/@relation/,/@data/ { print $0 >> Trainf;  
                      print $0 >> Testf; 
                      next 
                    }
                    { Line[rand()] = $0; 
                      Lines++ 
                    }
END { 
  Start = Lines/Bins * (Bin - 1) ;
  Stop  = Lines/Bins * Bin;
  for(I in Line) {
    N++;
    What = (N>= Start && N < Stop) ? Testf : Trainf
    print Line[I]>>What; }
}