Well,
I understand that I can do this, and I have. What I find as strange is the
differences in the data access between the TChain and the TTree. If I open
the file with TFile I can access the data by creating a variable placeholder,
telling the TTree the address of the placeholder and then pulling the right
entry. Now, if I open the data through the TChain, there are some more
detail to take care of. I am reading about them but do not follow them. I
understand that the TChain is based off of TTree, so, intuitivly I would
assume that it would work transparently as a tree also, such is not the case.
The main thing that bothers me is that in the class header that was created
with makeclass, it declares a lot of variables, all the information that I am
looking for and it seems to make sence. Then, instead of calling
SetBranchAddress over and over it just calles this on a few of the variables
in the TTree. After makeing the call to GetEntry all the data seems filled
even though it seems that the TTree was never passed references to the
declared placeholders.
Justace
On Sunday 17 August 2003 03:34 pm, zaldy wrote:
> Hi,
>
> If I understood it correctly; you want to chain 4 root files, say
> file1.root, file2.root, file3.root, and file4.root, then you want to
> produce a code using the MakeClass Functionality.
>
> If this is the case, one possibility is:
>
> At the directory where all these root files are located do:
> root[] TChain ch("SMT");
> root[] ch.Add("file*.root");
> root[] SMT->MakeClass("myClass");
>
> Assuming the root files are of same tree structure, the above lines should
> result to the creatioin of myClass.C and myClass.h.
> Then you can edit/modify the files according the nature of your
> application.
>
> I you want to understand the meaning of the codes and functions in the
> TChain class I suggest you go to the site:
>
> http://root.cern.ch/root/html/TChain.html
>
> Hope it helps...keep trying.
>
> On Sun, 17 Aug 2003, Justace Clutter wrote:
> > I am a very new root user and have been trying to understand how the
> > TChain works. There is a TTree, called SMT, spread out among four
> > different root files. If I load the first file up using just a straight
> > TFile I can access the data directly like the following:
> >
> > Int_t fdisk01_wedge01_n[768];
> >
> > SMT->SetBranchAddress("fdisk01_wedge01_n", &fdisk01_wedge01_n);
> > SMT->GetEntry(0);
> >
> > However when I try to load all the data at once with TChain I get very
> > confused.
> >
> > TChain *data_chain = new TChain("SMT");
> >
> > data_chain->Add("file1");
> > data_chain->Add("file2");
> > data_chain->Add("file3");
> > data_chain->Add("file4");
> >
> > At this point I can not just run the same code as I did above. Now I ran
> > the makeclass utilities and generated the class files, but now I am even
> > more confused. The variables are declared in the class but only a few
> > are set through the SetBranchAddress functions. But they are all
> > available somehow.
> >
> > I know that this post is very confusing, but I am confused. I have went
> > through the ROOT Users Guide and the examples but they did not help my
> > understanding of this. Any help on this matter would be greatly
> > appreciated. I guess that I just want to know how it works, I could just
> > use the makeclass and close my eyes but that does not put a smile on my
> > face.
> >
> > Justace Clutter
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