Histogram from leaf of tree

ROOT
, ,
1

I have a root file with a tree. I need to write a macro to access the histogram from the tree.
Opening the root file in the terminal and using the command
tree.Draw(“leafname”)
gives me the histogram.

But I need to write a macro and access the histogram.

Thanks!

2

See “Retrieving the result of Draw” in: TTree::Draw

3 
tree.Draw("leafname");
auto h1 = (TH1F*)gPad->GetPrimitive("htemp");
4

No I am getting some error.

image
image1797×415 83.1 KB

I am trying something like this:

TLeaf *leaf = tree->GetLeaf(“Mult”);
for (Int_t i=0; i<entries; i++){
leaf->GetBranch()->GetEntry(i);
myhist->Fill(leaf->GetValue());
}
myhist->Draw();

5

You have the wrong quotes:
try:

TLeaf *leaf = tree->GetLeaf("Mult");
6

TH1F *myhist = new TH1F();
TLeaf *leaf = tree->GetLeaf(“Mult”);
for (Int_t i=0; i<entries; i++){
leaf->GetBranch()->GetEntry(i);
myhist->Fill(leaf->GetValue());
}
myhist->Draw();

I tried but I am getting empty histogram. I copied that line of code. (quotes line)

7

Can you post something complete we can run ? for instance, in your example we do not know what entries is…

8

The root file that I am using is large. But here is the link.
https://drive.google.com/file/d/1KEwynNDrXrOGenniBhYhZFwGuFHTtAAu/view?usp=sharing
A1.C (4.6 KB)

9

All your data are in Overflow. You did not specify the histogram limits.

Screenshot 2022-10-06 at 17.15.08
Screenshot 2022-10-06 at 17.15.081306×896 21.8 KB

10

Any solution for that?

11 
   double xmin = ???? ;// should be defined
   double xmax = ???? ; // should be defined
   int nbins = ???; // should be defined
   TH1F *myhist = new TH1F("myhist", "myhist", nbins, xmin, xmax);
12

So can I obtain those values from the command line. Like when I use the command line and open the root file and draw the histogram using tree.Draw(“leafname”) command.

13

Try with:
TH1F *myhist = new TH1F("myhist", "myhist", 100, 0., 0.); // automatic binning

14

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image750×184 24.8 KB

image
image
image1910×718 70.9 KB

Screenshot from 2022-10-06 22-23-45
Screenshot from 2022-10-06 22-23-451910×718 78.5 KB

c1
c11918×992 10.6 KB

Okay so I have some doubts. In the first picture when I do .ls, there are two trees. current cycle and backup cycle. I don’t understand why.
And I find two different histograms with different number of entries by viewing it in TBrowser l.
But using the macro and finding the histogram it gives me 10000 entries (c1.png).

15