Hi,
With ROOT in the CVS repository you can now draw TBits objects, with
mytree.Draw("myEventBits") or with a click on an unsplit branch containing a
TBits.
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.
After much thought, we decided not to implement the operator[] for TBits
because it introduced more confusion than it solved problem. In order for
it to be useful, we need operator[int i] to return 0 or (i+1). We need
(i+1) because the bits range from 0 to N and we need to be able to
distinguish between bit[0] being on or off! If it returns (i+1), then the
histogram drawn would be, very counter-intuitively, ranging from 1 to N+1,
problem which we would have wanted to fix with yet another special case.
So instead we implemented drawing a TBits objects by itself (code which
could be extended to allow the special drawing of other classes).
Please let us know if this is sufficient.
Cheers,
Philippe.
-----Original Message-----
From: Birger Koblitz [mailto:koblitz@mail.desy.de]
Sent: Friday, January 17, 2003 3:26 AM
To: Rene Brun
Cc: Philippe Canal; Andreas Meyer; Ursula Berthon
Subject: RE: [ROOT] Feature Requests for TBits (fwd)
Hi,
I would really like to have the operator [] in TBits because this allows
very easy access to the individual bits and many other
bitfield-implementations do it like this. Phillipes suggestion to return
the bitnumber is a very good idea, since the return value would still be
"true" or "false" as of the C-convention while providing the necessary
information for drawing. Using simply the Draw method is also to be
favoured because this is what beginners would try first.
Cheers,
Birger
On Thu, 16 Jan 2003, Rene Brun wrote:
> Hi Philippe,
>
> One could implement the operator [] in TBits, but after thinking,
> it would be more appropriate to implement in TH1
> Int_t TH1::Fill(TBits &bits);
>
> This function could do the loop automatically.
>
> Rene
>
> On Thu,
> 16 Jan 2003, Philippe Canal wrote:
>
> > Hi,
> >
> > > - 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.
> >
> > If this really the intent, this is a departure from the usual semantic
of
> > the Draw command in regard to an array of values. Typically for array
> > of values, the values themself are plotted (basically doing a series of
> > h->Fill(arr[i]) ). In the above description, it seems that instead what
is
> > plotted is the 'index' of the value, i.e. if (arr[i]) h->Fill(i).
> >
> > This would complexify things because if you fill you want the formula to
> > return the index value but I you use it in an expression you would want
it
> > to return 0 or 1.
> >
> > This 'problem' is more or so resolved if TBits.operator[UInt bitnumber]
> > returns
> > either 0 (disabled bit) or bitnumber (enabled bit).
> >
> > What do you think?
> > Philippe.
> >
> >
> > -----Original Message-----
> > From: Rene Brun [mailto:brun@pcbrun.cern.ch]
> > Sent: Monday, December 02, 2002 4:21 PM
> > To: pcanal@fnal.gov
> > Subject: Re: [ROOT] Feature Requests for TBits (fwd)
> >
> >
> > Hi Philippe,
> >
> > About one month ago, there was an exchange of mails about TBits
> > and TTreeFormula. I forgot to discuss this (my answer) with you
> > this afternoon. Could you implement it?
> >
> > Rene
> >
> > ---------- Forwarded message ----------
> > Date: Thu, 31 Oct 2002 16:21:35 +0100 (MET)
> > From: Birger Koblitz <koblitz@mail.desy.de>
> > To: Rene Brun <brun@pcbrun.cern.ch>
> > Cc: Rene.Brun@cern.ch, roottalk@pcroot.cern.ch,
> > Andreas Meyer <ameyer@mail.desy.de>,
> > Ursula Berthon <berthon@poly.in2p3.fr>
> > Subject: Re: [ROOT] Feature Requests for TBits
> >
> > 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]");
> >
> > - Not only calling mytree.Draw("myEventBits"); should produce this
> > histogram, but also clicking on the variable in the TBrowser.
> >
> > 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
> >
> >
>
>
------------------------------------------------------------
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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