Extract a root file

[m_cern313]

Hello,
I have a huge root file having so many distributions. I would like to extract one distribution of them? I need your suggestion how to do that?

---

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

---

[Wile_E_Coyote]

rootls --help
rootcp --help

[m_cern313]

Sorry to explain you I need to write a macro?

[Wile_E_Coyote]

These are standalone executables delivered with ROOT 6.

[m_cern313]

Thanks yes that’s true but I want to do it in a macro. I wrote macro in this way. Tell me further what i should do to write my specific distribution in a current directory

TFile* myfile = TFile::Open(“filename.root”,“READ”);
TH1F* myhist = (TH1F*) myfile->Get(“name_of_the_histogram_in_the_Tree”);

[Wile_E_Coyote]

ROOT How To -> Input/Output -> How to Write Objects to a File?

[m_cern313]

TFile* myfile = TFile::Open(“filename.root”,“READ”);
TH1F* myhist = (TH1F*) myfile->Get(“name_of_the_histogram_in_the_Tree”);
myhist->Write();

Sorry to continue with my method please tell what is wrong with this that i can write the histogram?

[Wile_E_Coyote]

ROOT Primer -> File I/O and Parallel Analysis -> Storing ROOT Objects

In a Nutshell -> Input and Output

[m_cern313]

This is my macro Please suggest me what is wrong with this:

#include<iostream>
using namespace std;
void sf()
{

TFile *myfile=TFile::Open("/storage/local/home/atlas/msohail/trigger_analysis/hist-tot22.root","RECREATE");
TH1F *myhist = (TH1F*)myfile->Get("PREtrigger_1Ele_And_1Ele3Jet_bjets_gt_2");
myhist->Write();

}

[couet]

The TFile command is launched with the option RECREATE so a new empty file will be created, therefore the next command doing the “Get” on this newly created file cannot work as you are trying to get something from an empty file.

[m_cern313]

If I replace RECREATE by READ?

[couet]

For instance … and check the file is not empty.

myfile->ls();

[m_cern313]

I checked It is not empty.

[couet]

May be the simplest will be to use the rootcp command:

$ rootcp --recreate /storage/local/home/atlas/msohail/trigger_analysis/hist-tot22.root:PREtrigger_1Ele_And_1Ele3Jet_bjets_gt_2  newfile.root