example.C

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#include "TRInterface.h"

// simple example on how to use ROOT-R interface

void example() {

    auto r = ROOT::R::TRInterface::Instance();
    // print R version
    r.Execute("print(version$version.string)");

    // compute standard deviation of 1000 vector normal numbers

    double std_dev_r  = r.Eval("sd(rnorm(1000))");
    std::vector<double> v = r.Eval("rnorm(1000)");
    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 
    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
    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

    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 forund in r = %f and ROOT = %f", value_r, value_root);

    
}