Creating histogram and daatset from ascii file

ROOT
1

Hi, I have an ascii file with content (for example)
2.0 7800.0 105.0
3.0 3690.0 70.0
4.0 1643.0 46.0
5.0 735.0 40.0
6.0 360.0 21.0

The 2nd column is number of events and 3rd column is error on number of events…

The first column is bin number, e.g. there are 7800 events between x-value 1.5 to 2.5, so i have put it as bin number 2.

There are 3690 events with x-avalue between 2.5 to 3.5…so i put it as bin number 3…

(1) How do i create a histogram where it would have 7800 entries for bin-2 and 3690 entries in bin 3 and so on… Also incorporate the error in entries in y-axis also.

(2) How do i make roodataset out of this ascii file so that i can fit it with some function…

-sanjay

2

Try:

{
  TGraphErrors *g = new TGraphErrors("AsciiFile.txt", "%lg %lg %lg");
  // for (Int_t i = 0; i < g->GetN(); i++) (g->GetEX())[i] = 0.5; // X errors
  g->SetNameTitle("g", "My data set;bin centre;number of events");
  g->Fit("expo"); // "expo" = "exp([Constant] + [Slope] * x)"
  gStyle->SetOptFit();
  g->Draw("AP");
}