inspired by the mail below from Thierry to roottalk I tried this on my on.
As described Tree::Draw works fine with methods of the event class. And
"when I add a cut, I just change the shared library"
is very nice.
But Tree::Draw does not work on public data elements of the event class.
Using the for everyone available program
$ROOTSYS/test/Event and
$ROOTSYS/test/libEvent.so
the problem shows as the follwing:
----------------------------------------------------------------------
$ROOTSYS/test/Event 400 1 0 1
^
split = 0
----------------------------------------------------------------------
root [0] gSystem->Load("libEvent.so");
root [1] TFile *f = new TFile("Event.root");
root [2] T->Draw("event.GetNtrack()");
Warning in <MakeDefCanvas>: creating a default canvas with name c1
// T->Draw("event.GetNtrack()") seems to work well
root [3] T->Draw("event.fNtrack");
*** Break *** segmentation violation
Error: No symbol T->Draw("event.fNtrack") in current scope FILE:./08870faa LINE:1
*** Interpreter error recovered ***
root [5]
----------------------------------------------------------------------
(root 2.00/13 for Linux RH 4.2, AIX 4.1)
Do I have to write get-functions for each data element of the event class?
Thanks and best regards,
Ludger
+-------------------------------------------------------------------+
| Ludger Janauschek email: janausch@mppmu.mpg.de |
| Max-Planck-Institut fuer Physik |
| (Werner-Heisenberg-Institut) phone: +49 89 32354 - 344 |
| Foehringer Ring 6 fax: +49 89 32354 - 213 |
| D-80805 Muenchen |
+-------------------------------------------------------------------+
On Thu, 3 Sep 1998, T Auger wrote:
> [...snip...]
>
> It makes a lot of sense to be able to add leaves to a tree after it
> was created, at one point I wanted to do that myself. However, I use a
> different approach which can be useful for small event size type analysis.
> To be able to use the tree.Draw() function and make cuts on it, I
> defined a Event class which does contain method returning invariant
> masses, missing masses, angles for certain type of particle, etc... :
>
> Float_t TClasEvent::InvM_gp() {
> ...
> return(inv_mass);
> }
>
> Then when creating the tree, I use the split switch set to 0. That
> way, the event is saved as a TObject and is no longer a collection of
> leaves. Then when I want to draw a quantity I simply need to call the
> method I defined InvM_gp() like that :
> T.Draw("event.InvM_gp()","event.InvM_gp()>0&&event.Mm_ppip()>0.5")
>
> All of that works because I store the event with the non-split method.
>
> Therefore, I do not want to store these kinematic quantities anymore
> since I can recalculate them on the fly.
> Of course the drawback is that I have to read back the entire event
> from the file which means that it takes longer to draw my
> histograms. But I still prefer it because, I do not need to re-create
> my tree when I add a cut, I just change the shared library TClasEvent that I
> created.
>
> hope this helps,
> Thierry
>