Make a random numbers .dat file

[Marooz_Malik]

Hello,
Can anybody here help me with generating random numbers and then saving them in a .dat file ?

[bellenot]

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <ctime>

int main(int argc, char* argv[])
{
   std::srand(std::time(nullptr));
   std::ofstream myfile;
   myfile.open("rnd_numbers.dat");   
   for (int i=0; i<100; ++i)
      myfile << std::rand() << std::endl;
   myfile.close();
   system("pause");
   return 0;
}

[behrenhoff]

Read http://www.cplusplus.com/reference/random/
and/or watch: https://channel9.msdn.com/Events/GoingNative/2013/rand-Considered-Harmful
In ROOT, you can also use TRandom3 (Mersenne Twister).

[Wile_E_Coyote]

#include "TRandom.h"
#include <fstream>

void random(void) {
  std::ofstream ofs("random.dat", std::ofstream::out);
  gRandom->SetSeed(0); // make it really random
  for (int i = 0; i < 1000; i++) ofs << gRandom->Rndm() << std::endl;
  ofs.close();
}

[Marooz_Malik]

It worked . Thank you.
Can you tell me how i can make a histogram with this .dat file ?

[Wile_E_Coyote]

root-forum search “ReadFile”

#include "TTree.h"
#include "TH1.h"

void draw(void) {
  TTree *t = new TTree("t", "temoporary tree with velocities");
  t->ReadFile("random.dat", "v/D");
  TH1D *h = new TH1D("h", "histogram;random;n", 100, 0.0, 1.0);
  t->Project("h", "v");
  delete t; // no longer needed
  h->Draw("L");
}

[Marooz_Malik]

It did worked but it is showing a blank plot with just x and y axis . Am i doing something wrong ?

[Danilo]

Hi,

is there a reason why you want to work with ascii files rather than optimised ROOT files?

D

[Marooz_Malik]

Hhhh Dpiparo, Actually I am going to work with AMPT model . So, I am learning how to deal with .dat files before starting my work. That’s my job. hh
Thanks for asking .

[Danilo]

Hi,

thanks, I see. I attach* a complete example which allows you to write and read data in dat format and analyse it “the modern way”, with TDataFrame.

The advantages of this setup, in my opinion, are:

• if needed, to analyse your data in parallel
• dump your datasets in ROOT format
• preserve your entire analysis in case you switch to another file format (e.g. ROOT)
• more concise way of expressing the analysis with a declarative approach

Cheers,
D

using namespace ROOT::Experimental;

// Configuration
auto nNumbers = 1024;
auto seed = 1;
auto filename = "random.dat";

void write()
{
   std::ofstream ofs(filename, std::ofstream::out);
   TRandom3 myGen(seed);

   auto printNumber = [&]() {
      ofs << myGen.Rndm() << std::endl;
   };

   TDataFrame f(nNumbers);
   f.Foreach(printNumber);

   ofs.close();
}

void read()
{
   auto f = TDF::MakeCsvDataFrame(filename, false); // we have no header
   auto h = f.Histo1D("Col0"); // the dat file has no header, the name of the column is Col0
   TCanvas c;
   h->Draw();
   c.Print("myHisto.png");
}

void readWrite()
{
   write();
   read();
}