ROOT::R::TRInterface &r=ROOT::R::TRInterface::Instance();

TRandom rg;
std::vector<Double_t> x(10),y(10);
for(int i=0;i<10;i++)
{
   x[i]=i;
   y[i]=rg.Gaus();
}

r["x"]=x;
r["y"]=y;

if (!gROOT->IsBatch() )  {

   r<<"dev.new()";//Required to activate new window for plot
   //Plot parameter. Plotting using two rows and one column
   r<<"par(mfrow = c(2,1))";

   //plotting the points
   r<<"plot(x, y, main = 'approx(.) and approxfun(.)')";

   //The function "approx" returns a list with components x and y
   //containing n coordinates which interpolate the given data points according to the method (and rule) desired.
   r<<"points(approx(x, y), col = 2, pch = '*')";
   r<<"points(approx(x, y, method = 'constant'), col = 4, pch = '*')";
}
else {
   r << "print('Interpolated points')";
   r << "print(approx(x,y,n=20))";
}

r<<"f <- approxfun(x, y)";

r<<"fc <- approxfun(x, y, method = 'const')";

if (!gROOT->IsBatch() ) {
   r<<"curve(f(x), 0, 11, col = 'green2')";
   r<<"points(x, y)";

   r<<"curve(fc(x), 0, 10, col = 'darkblue', add = TRUE)";
   // different interpolation on left and right side :
   r<<"plot(approxfun(x, y, rule = 2:1), 0, 11,col = 'tomato', add = TRUE, lty = 3, lwd = 2)";
}
else {
   r << "x2=x+0.5";
   r << "print('Result of approxfun with default method')";
   r << "print(paste('x = ',x,'  f(x) = ',f(x2)))";
   r << "print('Result of approxfun with const method')";
   r << "print(paste('x = ',x,'  f(x) = ',fc(x2)))";
}