# Example¶

Simple example on how to use ROOT-R interface.

Author:
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Sunday, September 19, 2021 at 08:23 AM.

In [ ]:
%%cpp -d
#include "TMath.h"
#include "Math/PdfFunc.h"
#include "TMatrixD.h"
#include "TError.h"
#include <array>
#include <vector>
#include "TRInterface.h"

In [ ]:
ROOT::R::TRInterface &r = ROOT::R::TRInterface::Instance();


Print r version

In [ ]:
r.Execute("print(version\$version.string)");


Compute standard deviation of 1000 vector normal numbers

In [ ]:
double std_dev_r  = r.Eval("sd(rnorm(10000))");
std::vector<double> v = r.Eval("rnorm(10000)");
double std_dev_root = TMath::StdDev(v.begin(),v.end());
std::cout << "standard deviation from R    = " << std_dev_r << std::endl;
std::cout << "standard deviation from ROOT = " <<  std_dev_root << std::endl;
if (!TMath::AreEqualAbs(std_dev_r,std_dev_root,0.1))
Error("ROOT-R-Example","Different std-dev found");


Use << to execute the r command instead of execute

In [ ]:
r << "mat<-matrix(c(1,2,3,4,5,6),2,3,byrow=TRUE)";
TMatrixD m = r["mat"];
std::array<double,6> a = r.Eval("seq(1:6)");
TMatrixD m2(2,3,a.data());

if  (!(m==m2)) {
Error("ROOT-R-Example","Different matrix  found");
m.Print();
m2.Print();
}


Example on how to pass root objects to r

In [ ]:
std::vector<double> v_root{1,2,3,4,5,6,7,8};
r["v"] = v_root;
r << "v2<-seq(1:8)";
bool isEqual = r.Eval("prod(v==v2)");
if (!isEqual) {
Error("ROOT-R-Example","Different vector created");
r << "print(v)";
r << "print(v2)";
}


Example on how to pass functions to r

In [ ]:
r["gaus_pdf"] = ROOT::Math::normal_pdf;

r << "y<-gaus_pdf(0,1,1)";
double value_r = r["y"];
double value_root = ROOT::Math::normal_pdf(0,1,1);
std::cout << "Function gaussian(0,1,1) evaluated in  R    = " << value_r << std::endl;
std::cout << "Function gaussian(0,1,1) evaluated in ROOT  = " <<  value_root << std::endl;
if (value_r != value_root)
Error("ROOT-R-Example","Different function value found in r = %f and ROOT = %f", value_r, value_root);