Show event by event from leaf

Newbie
1

Hi, I am trying to draw two leafs (leaf1 vs leaf2) in a branch of tree. I managed to draw all entries together using:

  f = new TFile("myfile.root");
  if ((!f) || f->IsZombie()) {delete f; return;} 
  f->GetObject("mytree", t);
  if (!t) {delete f; return;} // just a precaution
  gROOT->cd();

  TTree *gt = (TTree *) f->Get("mytree");

  TH2D *h2 = new TH2D("h2", "tracks;x;z", 100, -100, 100, 100, -100, 100);
  h2->Sumw2(kTRUE);
  
  t->Project("h2", "leaf1:leaf2", "");

  delete f;

  h2->Draw("COL");
  h2->SetStats(0); //hide stats

But what I see is all events (entries from both leafs drawn. How do I filter to see event by event?

2

What do you mean exactly ? the Project command will fill h2 with leaf1 and leaf2 along x and y axis… I am not sure "event by event"mean is that case.

3

Attached is what I get. They are 100 events. I would like to show only one event if possible.

For example:

I wanted to loop over all entries in my tree and draw only one by one but it didn’t work and it showed the same result:

  //for (int i=0;i<events;i++){
	//  cout<<"Event "<<i<<endl;
	//  gt->GetEntry(i);
	//  TH2D *h2 = new TH2D("h2", " tracks;x;z", 100, -100, 100, 100, -100, 100);
	//  h2->Sumw2(kTRUE);
	//  t->Project("h2", "leaf1:leaf2", "");
4

Have a look at the 2 last parameters of TTree::Project. The number of event and the last event. Use it to select on 1.

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