Re: Data shuffling

Put your 20M objects (say TVectorD) in a TObjArray and use TObjArray::Randomize
see: http://root.cern.ch/root/html/TObjArray.html#TObjArray:Randomize

Rene Brun

On 28/10/2010 15:13, Dr Ian Korir wrote:
>
> Dear ROOTers,
>
> This is a very basic questions. I have about 20M 1D array of integers
> (which actually representing cells of larger arrays data structures)
> and want to increase the entropy or randomness of the data. This may
> mean shuffling at least 20M!/2 times in the ideal situation even
> though basic maths says only 6 or 7 will do. This could probably take
> a century or so with a standard workstation.
>
> Now here comes my question, which is the most optimum way of doing the
> shuffling for timely reason?
>
> My present algorithm goes like this for 1000 shuffles of the cell
> locations:
>
> //--------------------------------------------------------------------
>
> TRandom3 gRan;
>
> gRan.SetSeed(0);
>
> const Int_t UWL = 20000000;
>
> Int_t dd1[UWL];
>
> Int_t dd2[UWL];
>
> Int_t i;
>
> Int_t is;
>
> Int_t LOOP = 500;
>
> for (i=0;i<UWL;i++) dd1[i]=i+1;
>
> printf("\n===================== Shuffling for %i Event
> =====================", LOOP);
>
> while (LOOP-->0){
>
> for (i=0;i<UWL;){
>
> is=gRan.Integer(UWL);
>
> if (dd1[is]>0) {dd2[i]=dd1[is]; dd1[is]=-1;i++;}
>
> }
>
> for (i=0;i<UWL;){
>
> is=gRan.Integer(UWL);
>
> if (dd2[is]>0) {dd1[i]=dd2[is]; dd2[is]=-1;i++;}
>
> }
>
> printf("\nShuffling @ event %i ", LOOP);
>
> }//for LOOPS
>
> //--------------------------------------------------------------------
>
> Is there a simpler and faster approach in root to perform such kind of
> entropy increase?
>
> On another note, which is faster to perform data synthesise, use of
> store data in say TH1F or routine arrays, given same data sizes?
>
> Regards,
>
> Ian
>
Received on Thu Oct 28 2010 - 15:24:00 CEST