Read a histogram

[Manuel_Torres]

Hello all,

I was trying to open a histogram in a macro, I followed this solution

Read a histogram from a ROOT file

Hi all, I have a root file with inside histograms, now I would like to open this file and to see an histogram, that I know the name of this histogram in the file. I red the “HowTo’s”, but I alway obtain an error. My code is: [code]{ TFile *f = new TFile(“myfile.root”); f.ls(); TH1F * h1 = new TH1F(“h1”,“h1 title” , 100, 0, 4); h1 = (TH1F*)f.Get(hist1); h1->Draw(); }[/code] with the comand f.ls I obtain this: KEY: TH1F hist1;1 Hist1 KEY: TH1F hist2;1 Hist2 KEY: TH1F hi…

Read histogram from file

Hi, Don’t write your own main() unless you really have to. You are missing an event loop; you want GUI interaction - all of that is provided if you run your code in ROOT, instead of building your own main(). (You’re missing a TApplication object; its Run() method creates an event loop.) Axel.

Draw a Histogram from within a root Macro

Hi Chris, you should specify the correct type of object you are reading from the file. In addition, you need to invoke the Draw method of TH1F/D: please refer to root.cern.ch/doc/master/classTH1F.html Assuming that the histogram is a TH1F (it could be a TH1D, it depends on who wrote it): TFile f(newrootpath); TH1F* T = NULL; f.GetObject("pedestal", T); T.Draw(); Cheers, D

but in all the cases show me this error

and this is my histogram

how can I fix this problem?

TFile *f1 = new TFile("1cut.root");

 TH1F* h1 =(TH1F*)f1->Get("MVA_BDT");
 h1->Draw();

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Please read tips for efficient and successful posting and posting code

ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

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[yus]

Hi Manuel,

based on your screnshot, the MVA_BDT histogram is located in the TMVAppbdt1.root, but your code

TFile *f1 = new TFile("1cut.root");

tries to open a different file. Why?
It’s usually a very good idea to check if your file exists, can be opened, and does contain the wanted histogram. To do this you should modify your code to something like this:

TFile *f1 = TFile::Open("1cut.root");
if (!f1 || f1->IsZombie())
{
    printf("f1 can not be opened\n");
    return;
}
TH1F* h1 = static_cast<TH1F*>(f1->Get("MVA_BDT"));
if (!h1)
{
    printf("MVA_BDT can not be fetched from f1\n");
    return;
}

[Manuel_Torres]

yes thanks, I was very distracted and tired , sorry for posting that noob question hahaha