Append to already saved ntuple

ROOT
1

Hi,

is it possible to append new entries to an ntuple, which has already been saved to a root file? So, open the root file, access the ntuple and append new entries to the existing ones.

thanx,
Balint

2

Simply open the file in "update"mode, read the Tree header in memory
andcontinue to fill.

Rene

3

It surely doesn’t work in this way:

#include <TNtuple.h>
#include <TFile.h>

void size(){

TNtuple * data1 = new TNtuple(“data”, “data”, “x:y”);

for(int i = 0; i < 1000; i++){
data1->Fill(gRandom->Rndm(), gRandom->Rndm());
}
TFile * file1 = new TFile(“file1.root”, “recreate”);
data1->Write();
file1->Close();

TFile * file2 = new TFile(“file1.root”, “update”);
TNtuple * data2 = (TNtuple*)file2->Get(“data”);
for(int j = 0; j < 1000; j++){
data2->Fill(gRandom->Rndm(), gRandom->Rndm());
}

file2->Close();
}

After running this file1.root should have 2000 entries, but when checking it I got:

C:\Documents and Settings\Balint\Tif\HTiRydberg\PC\noclus>root.exe -l file1.root
root [0]
Attaching file file1.root as _file0…
root [1] .ls
TFile** file1.root
TFile* file1.root
KEY: TNtuple data;1 data
root [2] data->GetEntries()
(const Long64_t)1000
root [3]

So, what is the problem here?

Thanx,
Balint

4

You had several problems in your code. See working code below

[code]#include <TNtuple.h>
#include <TFile.h>

void size(){

TFile * file = new TFile(“file1.root”, “recreate”);
TNtuple * data = new TNtuple(“data”, “data”, “x:y”);

for(int i = 0; i < 1000; i++){
data->Fill(gRandom->Rndm(), gRandom->Rndm());
}
data->Write();
delete file;

file = new TFile(“file1.root”, “update”);
data = (TNtuple*)file->Get(“data”);
for(int j = 0; j < 1000; j++){
data->Fill(gRandom->Rndm(), gRandom->Rndm());
}

data->Write();
delete file;
}
[/code]

Rene

5

Thanx for the help. (I’ll read the docs, I promise, when I’ll have some spare time :slight_smile: )

Balint