Write a tree with input from a text file

ROOT
1

Hi

What I want to do, is to read a text file which includes x-secs for some processes and then and fill a tree . What I do is this


Double_t x_sec;
tree->Branch("x_sec",&x_sec,"x_sec/D");

#include <fstream>
#include <iostream>
 
string filename = "MyTextFile.txt";
vector<string> input_files;
 
ifstream textfile;
textfile.open(filename.c_str());
if( !textfile.good() ) {
  cerr << "Cannot open the file: \"" << filename+"\"!"<<endl;
  abort();
} 
 
// OK we have the file!
string line("");
while( !textfile.eof() ) {
  line="";
  textfile >> line;
 
   // Do your stuff here! maybe:
   if (line=="") continue;
   if (line== "#") continue;
   input_files.push_back(line);
}

How to take now the string from input_files which of type char and make it of type Double_t in order to write to tree ? (ie pass to and then write it to the x_sec ? )

Thanks in advance!

2

Hi,

Did you try TTree::ReadFile?

Philippe.

3

Yes, this worked now!!!

Thanks again Philippe

Would it be possible from this class do the following

read param1 and param2 which are given in the txt like

param1 = value1
param2 = value3
x_sec = cross

and plot the TH2D of x_sec as a func of param1:param2 ??

Thanks again!

4

see example in $ROOTSYS/tutorials/tree/cernbuild.C

Rene

5

Hi

I tried the

Tree *mtree;

mtree->Branch("m0", &m0,"m0/D");
mtree->Branch("m12", &m12,"m12/D");

mtree->ReadFile ("file.txt","m0");
mtree->ReadFile("file2.txt,"m12");

but it read correctly only for the 1rst created Branch ie m0 . How can I read multiple files and direct the to different branches ?

Thanks

6

Hi,

You will need to either use 2 distinct TTree or copy/paste and adapt the code in ReadFile. i.e. ReadFile assumes you are reading all the branches of the TTree.

Cheers,
Philippe.

7

Ok, thanks for this

Now, how is it possible the value I read from the m0.txt to pass it in an output .root file to be inlcuded in the name, something like

[code]ttree->ReadFile(“file.txt”,m0)

char name[30];
sprinf(name,"%d",m0);

string filename = “…/results/Tree”+name.c_str()+".root";

TFile *savefile = new TFile (“filename”);

[/code]

can this work somehow ?

thanks

8

Hi,

I am not sure what you tried nor exactly what you mean :slight_smile: but the following might be what you are looking for:void readOneVar(const char *txtfile, const char *varname) { TString filename; filename.Form( "../results/Tree%s.root", varname ); TFile *savefile = new TFile (filename); TTree *tree = new TTree("tree",""); tree->ReadFile(txtfile,varname); tree->GetCurrentFile()->Write(); }

Philippe.

9

Yes, I think you got the point ie to read a value from a txt file and save it as “extension” to the root file…

Thanks!