Plotting part of a txt file

Newbie
1

I’m doing a pretty easy task, but I can’t find a simple way to do this.
I want to plot only a part of a txt file, which looks like:

#First part
2		1.96E-02
4		2.57E-02
12		2.81E-02
20		3.12E-02
28		3.17E-02
35		3.19E-02
#Second part
30		3.16E-02
28		3.19E-02
34		3.22E-02
31		3.17E-02

For the moment the only solution I found was to split the file in two (part_1.txt, part_2.txt) and the do:

   TCanvas *c1 = new TCanvas("c1");
   c1->Divide(1,2);

   c1->cd(1);
   TGraphErrors *gr1 = new TGraphErrors("part_1.txt","%lg %lg");
   gr1->SetMarkerColor(kRed);
   gr1->SetMarkerStyle(20);
   gr1->Draw("AP");
   
   c1->cd(2);
   TGraphErrors *gr2 = new TGraphErrors("part_2.txt","%lg %lg");
   gr2->SetMarkerColor(kBlue);
   gr2->SetMarkerStyle(20);
   gr2->Draw("AP");

which looks like my desired result.
Is there a way to read (or plot) olny a part of a txt file, maybe using the range of rows?

2

In the TGraph constructor from a file there no parameter allowing to do that, like for instance a line number to start the reading. The file is always read completely. I think the best way in your case would be to do a classical C++ file reading and fill the TGraph with the points you want.