Draw X-Axis with specific values

[Assalmi]

Hello, I would like to plot three non-uniform points 0.025 0.1 0.125, I am trying to display on the X-axis only the points 0.025 0.1 0.125 or display a string value (0.5x0.5x0.1 0.5x0.5x0. 4 0.5 x0.5x0.5) respectively.
I had tried with the examples from the Forum but I could not find a good solution.

test.C

void test()
{

TGraph *g1 = new TGraph("aa.txt");
g1->SetMarkerStyle(20);
g1->SetMarkerColorAlpha(kBlue, 0.35);
g1->GetYaxis()->SetTitle("Y axis");
g1->GetXaxis()->SetTitle("X axis");
g1->SetMarkerSize(1);
TAxis *axis = g1->GetXaxis();
axis->SetNdivisions(5, kTRUE);
g1->Draw("APL");
}

aa.txt

0.025 0.3
0.1   0.83
0.125 0.98

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ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

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[dastudillo]

This is a slight modification of a macro found on this forum some time ago, so all credit goes to the original author, couet:

void aa()
{
  TGraph *g1 = new TGraph("aa.txt");
  g1->SetMarkerStyle(20);
  g1->SetMarkerColorAlpha(kBlue, 0.35);
  g1->GetYaxis()->SetTitle("Y axis");
  g1->GetXaxis()->SetTitle("X axis");
  g1->SetMarkerSize(1);

  g1->Draw("APL");
  g1->GetXaxis()->SetLabelSize(0);
  g1->GetXaxis()->SetTickLength(0);

  Int_t i,n;
  Double_t x,y;
  TLatex *t;
  TLine *tick;
  TLine *grid;
  double ymin = g1->GetHistogram()->GetMinimum();
  double ymax = g1->GetHistogram()->GetMaximum();
  double dy = (ymax-ymin);
  n = g1->GetN();
  for (i=0; i<n; i++) {
    g1->GetPoint(i,x,y);
    t = new TLatex(x, ymin-0.03*dy, Form("%4.3f",x));
    t->SetTextSize(0.03);
    t->SetTextFont(42);
    t->SetTextAlign(21);
    t->Draw();
    tick = new TLine(x,ymin,x,ymin+0.03*dy);
    tick->Draw();
    grid = new TLine(x,ymin,x,y);
    grid->SetLineStyle(3);
    grid->Draw();
  }
}

You can leave out the “grid” lines if not needed.
Edit - Original post:

A macro to Draw labels on graph points

root [0] double x[3] = {1,3,5} root [1] double y[3] = {1,5,2} root [2] auto gr = new TGraph(3,x,y); root [3] gr->SetMarkerStyle(20); root [4] .x DrawGraphWithLabelsOnPoints.C(gr) The points can be moved interactively. The labels follow. DrawGraphWithLabelsOnPoints.C (916 Bytes) [29]

[Assalmi]

thank you dastudillo It works well

[Assalmi]

Hello dastudillo now i have another question
I have 5 points in the X axis, each corresponding to a type eg A, B, C, D, E respectively. how can display A, B, C, D, E in X axis
Best regards
a.txt

1 1.5
2 2
3 1.2
4 4.3
5 2.7

[couet]

#include <stdio.h>

void a(){
   FILE *f = fopen("a.txt","r");

   char line[80];
   float x,y;
   auto g = new TGraph();
   int i=0;
   while (fgets(line,160,f)) {
      sscanf(line  ,"%g %g",&x,&y);
      g->SetPoint(i,y,x);
      i++;
   }
   fclose(f);
   g->Draw("AL*");
}

[Assalmi]

thank you couet for the reply,
I think I misexplained my question, The question is to display in X axis a string A, B, C, D, E, each for this string corresponding to a line in the a.txt file (see example in image below) .
Best regards

[couet]

void a(){
   auto g = new TGraph("a.txt");
   g->Draw("AL*");

   gPad->Update();
   TAxis *X = g->GetXaxis();
   X->SetNdivisions(9);
   X->ChangeLabel(1,-1,-1,-1,-1,-1,"A");
   X->ChangeLabel(2,-1,-1,-1,-1,-1,"B");
   X->ChangeLabel(3,-1,-1,-1,-1,-1,"C");
   X->ChangeLabel(4,-1,-1,-1,-1,-1,"D");
   X->ChangeLabel(5,-1,-1,-1,-1,-1,"E");
   gPad->Modified();
   gPad->Update();
}

[Assalmi]

thank you very much couet