How to save several trees in one file?

ROOT
1

Hello!

I have a lot of events (> 100 000).
I want to calculate some values (integral, for example), draw graphs and save all this information in a tree.
Individual tree for each event.
If I write one tree in one file I waste a lot of time for open and close operations.
So, the better solution to save several trees in one file.

Previously, I used tree.Write().

Now, as I understand (TTree.Write() vs. TFile.Write()), I have to use tfile.Write().

But I get this message: Warning in <TFile::Write>: file not opened in write mode.
And my file is empty.

My code:

#include <iostream>
#include <string>
#include <iomanip>


#include "TGraph.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TCanvas.h"
#include "TROOT.h"
#include "TRandom.h"

using namespace std;

int main(int argc, char *argv[])
{
    TFile f_tree;

    string s_output_file = "/home/darkside/Vlad_Programs/test.root";
    const int events_per_file = 2;
    const int n_events = 2;
    const int samp_per_event = 100;

    vector<double> xv;
    for (int i = 0; i < samp_per_event; ++i)
    {
        xv.push_back(i);
    }

    TRandom rnd;


    for(int file_i = 0; file_i < n_events; file_i++)
    {
        vector<double> yv;
        for (int i = 0; i < samp_per_event; ++i)
        {
            yv.push_back( rnd.Rndm() );
        }

        //I want to save "events_per_file" events per one file
        if(file_i % events_per_file == 0) f_tree.Open(s_output_file.c_str(), "RECREATE");

        TTree tree("t1", "Tree with result");

        double just_some_value = file_i;
        tree.Branch("just_some_value", &just_some_value, "just_some_value/D");

        TCanvas canv("c", "c", 0, 0, 1900, 1000);
        tree.Branch("canvas_tr", "TCanvas", &canv);

        TGraph graph_ch1(samp_per_event, &xv[0], &yv[0]);
        graph_ch1.Draw();

        tree.Fill();
        if(file_i % events_per_file == 0) f_tree.Write();
        if(file_i % events_per_file == 0) f_tree.Close();

    }


    cout << "all is ok" << endl;
    return 0;
}

Could you help me?

Thank you in advance.
Best regards, Vladislav.

2

Why do you want to have one tree for each event? Put everything in the same tree. Call Fill once per event.

3

The following version of your program does not produce the warning.

#include <iostream>
#include <string>
#include <iomanip>


#include "TGraph.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TCanvas.h"
#include "TROOT.h"
#include "TRandom.h"

using namespace std;

void vla()
{

    TFile *f_tree;

    string s_output_file = "/home/darkside/Vlad_Programs/test.root";
    const int events_per_file = 2;
    const int n_events = 2;
    const int samp_per_event = 100;

    vector<double> xv;
    for (int i = 0; i < samp_per_event; ++i)
    {
        xv.push_back(i);
    }

    TRandom rnd;


    for(int file_i = 0; file_i < n_events; file_i++)
    {
        vector<double> yv;
        for (int i = 0; i < samp_per_event; ++i)
        {
            yv.push_back( rnd.Rndm() );
        }

        //I want to save "events_per_file" events per one file
        if(file_i % events_per_file == 0) {
              f_tree = new TFile(s_output_file.c_str(), "RECREATE");
         }

        TTree tree("t1", "Tree with result");

        double just_some_value = file_i;
        tree.Branch("just_some_value", &just_some_value, "just_some_value/D");

        TCanvas canv("c", "c", 0, 0, 1900, 1000);
        tree.Branch("canvas_tr", "TCanvas", &canv);

        TGraph graph_ch1(samp_per_event, &xv[0], &yv[0]);
        graph_ch1.Draw();

        tree.Fill();
        if(file_i % events_per_file == 0) f_tree->Write();
        if(file_i % events_per_file == 0) f_tree->Close();

    }
}
4

Anyway, here a modified version of your code:

#include <iostream>
#include <string>
#include <iomanip>


#include "TGraph.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TCanvas.h"
#include "TROOT.h"
#include "TRandom.h"

using namespace std;

int test()
{
    

    string s_output_file = "test.root";
    const int events_per_file = 2;
    const int n_events = 2;
    const int samp_per_event = 100;

    vector<double> xv;
    for (int i = 0; i < samp_per_event; ++i)
    {
        xv.push_back(i);
    }

    TRandom rnd;

	
	TFile* f_tree = NULL;
	TTree* tree = NULL;
	
    for(int file_i = 0; file_i < n_events; file_i++)
    {
		double just_some_value = file_i;
		vector<double> yv;
        for (int i = 0; i < samp_per_event; ++i)
        {
            yv.push_back( rnd.Rndm() );
        }
		TCanvas canv("c", "c", 0, 0, 1900, 1000);
		TGraph graph_ch1(samp_per_event, &xv[0], &yv[0]);
        graph_ch1.Draw();

		if(file_i % events_per_file == 0) 
		{
			f_tree = TFile::Open(s_output_file.c_str(), "RECREATE");
			tree = new TTree("t1", "Tree with result");
			tree->Branch("just_some_value", &just_some_value, "just_some_value/D");
			tree->Branch("canvas_tr", "TCanvas", &canv);
		}
        
        
        //I want to save "events_per_file" events per one file        
        tree->Fill();
        
        if(file_i % events_per_file == events_per_file-1) 
		{
			f_tree->Write();
			f_tree->Close();
			delete f_tree;
			f_tree = NULL;
			tree = NULL;
		}
    }

	if(f_tree)
	{
		f_tree->Write();
		f_tree->Close();
		delete f_tree;
		f_tree = NULL;
		tree = NULL;
	}

    cout << "all is ok" << endl;
    return 0;
}
5

I am not specialist in root trees. May be your variant is better.

In any case, how to save root tree?

As I understand your variant is to put TTree tree("t1", "Tree with result"); outside the loop.
This code (one tree with per file) has the same error:

#include <iostream>
#include <string>
#include <iomanip>


#include "TGraph.h"
#include "TFile.h"
#include "TRandom.h"
#include "TTree.h"
#include "TCanvas.h"
#include "TROOT.h"
#include "TRandom.h"

using namespace std;

int main(int argc, char *argv[])
{
    TFile f_tree;
    TTree tree("t1", "Tree with result");


    string s_output_file = "/home/darkside/Vlad_Programs/test.root";
    const int events_per_file = 2;
    const int n_events = 2;
    const int samp_per_event = 100;

    vector<double> xv;
    for (int i = 0; i < samp_per_event; ++i)
    {
        xv.push_back(i);
    }

    TRandom rnd;


    for(int file_i = 0; file_i < n_events; file_i++)
    {
        vector<double> yv;
        for (int i = 0; i < samp_per_event; ++i)
        {
            yv.push_back( rnd.Rndm() );
        }

        //I want to save "events_per_file" events per one file
        if(file_i % events_per_file == 0) f_tree.Open(s_output_file.c_str(), "RECREATE");



        double just_some_value = file_i;
        tree.Branch("just_some_value", &just_some_value, "just_some_value/D");

        TCanvas canv("c", "c", 0, 0, 1900, 1000);
        tree.Branch("canvas_tr", "TCanvas", &canv);

        TGraph graph_ch1(samp_per_event, &xv[0], &yv[0]);
        graph_ch1.Draw();

        tree.Fill();
        if(file_i % events_per_file == 0) f_tree.Write();
        if(file_i % events_per_file == 0) f_tree.Close();

    }


    cout << "all is ok" << endl;
    return 0;
}
6

The version I posted does not have the error

7

Many thanks!
When I was writing my post you sent the answer.

8

Dear ferhue, many thanks for your help!
I had also several errors in my code, but you fixed them.

1 Like