Re: [ROOT] Feature Requests for TBits

From: Rene Brun (Rene.Brun@cern.ch)
Date: Thu Oct 31 2002 - 16:30:41 MET


Hi Birger,

On Thu, 31 Oct 2002, Birger Koblitz wrote:

> Hi Rene,
> 
> yes, this is what we would like to have. Sorry for my poor description.
> Just two additional clarifications:
> - The operator [] should also work in selections:
>   mytree.Draw("somethingElse","myEventBits[10]");
> 

Yes, this was implicit in my previous mail. In the selection, mask
operations should also be supported, eg
    mytree.Draw("somethingElse","myEventBits & 0x3ff");

> - Not only calling mytree.Draw("myEventBits"); should produce this
>   histogram, but also clicking on the variable in the TBrowser.

Yes, it is the same logic. TBrowser calls TTree::Draw.

OK, we will implement this logic. Could you send me a small TTree file
(not HAT file) that we could use to test the new feature?

Rene Brun


> 
> Cheers,
>   Birger
> 
> 
> On Thu, 31 Oct 2002, Rene Brun wrote:
> 
> > Hi Birger,
> >
> > Let see if I understand correctly your request.
> >
> >  - you are requesting an operator [] to get the ith bit in a TBits
> >    instead of calling the function TestBitNumber().
> >    That is quite easy to implement. I propose in this case
> >    a read only operator [].
> >
> >  - you want to do mytree.Draw("myEventBits");
> >    This will automatically loop on all your events and filling
> >    an hitogram with as many channels as there are bits in TBits
> >    and where the bin count is incremented by 1 or the specified weight
> >    for each event where the corresponding bit is set.
> >    This requires a bit more work, but I agree would be a nice addition.
> >
> > Rene
> >
> > On Thu, 31 Oct 2002, Birger Koblitz wrote:
> >
> > > Hi Rene,
> > >
> > > I think Ursula Berthon already talked to you about this at the
> > > Root-Meeting:
> > >
> > > Within H1 we would like to be able to put bit-arrays into our HAT tree
> > > which should be accessible using only a browser and which is used for
> > > event selection. Currently TBits allows to use the member function
> > > TestBitNumber() which is quite inconvenient if it comes to a selection of
> > > a large number of status bits e.g. to check if the quality of an event is
> > > good. This could easily go over the maximum selection length of a tree.
> > > Therefore it would be nice if one could simply use bits[i] to check the
> > > ith bit in TBits bits. In addition it would be nice if one could view a
> > > bit-array in a TBrowser. It should show a histogram over the bits and the
> > > number of entries per bit. Currently fAllBits shows the entries (in 2^i
> > > form) for the lowest byte. I think this is not really useful.
> > >
> > > In the moment we are using byte-arrays which at least allow to use the []
> > > operator and allow us to inspect one bit with the TBrowser. H1 would be
> > > very intersted to move to TBits because currently the bit-arrays make up
> > > most of our HAT ntuple, we would be even willing to move to a newer
> > > root-version ;-)
> > >
> > > Cheers,
> > >   Birger
> > >
> > >  ------------------------------------------------------------
> > >  Birger Koblitz                          koblitz@mail.desy.de
> > >  MPI für Physik
> > >  c/o DESY-FH1                           Tel: +49 40 8998-2431
> > >  Notkestr. 85                           Fax: +49 40 8998-3094
> > >  D-22603  HAMBURG
> > >
> >
> >
> 
>  ------------------------------------------------------------
>  Birger Koblitz                          koblitz@mail.desy.de
>  MPI für Physik
>  c/o DESY-FH1                           Tel: +49 40 8998-2431
>  Notkestr. 85                           Fax: +49 40 8998-3094
>  D-22603  HAMBURG
> 



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