Plotting ASCII files in ROOT

Question

I am trying to write a small macro that reads data from an ASCII file that has 4 columns. But I want to graph only the second the third columns as (x, y).

Answer 1

You can use the "CSV Contructor" as shown above or simply generate an empty TGraph (or TGraphErrors), loop over your CSV file and add points. Example with some constant error bars given in the first line/header:

    ifstream infile("input.csv");

    TGraphErrors *g1 = new TGraphErrors();
    g1->SetName("name_for_graph");
    g1->SetTitle("Title for your Graph;x values [x unit];y values [y unit]");

    Int_t pt=0, nv=0;
    Double_t e_vc=0.;
    Double_t vs=0., vc=0.;

    infile >> e_vs >> e_vc;

    while (1) {
            if(!infile.good()) break;

            infile >> vs >> vc;

            g1->SetPoint(pt, vs, vc);
            g1->SetPointError(pt, e_vs, e_vc);
            pt++;
    }
    infile.close();

...

    g1->Draw("APX");