df005_fillAnyObject.C

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/// \file
/// \ingroup tutorial_dataframe
/// \notebook -draw
/// This tutorial shows how to fill any object the class of which exposes a
/// `Fill` method.
///
/// \macro_code
/// \macro_image
///
/// \date March 2017
/// \author Danilo Piparo

// A simple helper function to fill a test tree: this makes the example
// stand-alone.
void fill_tree(const char *treeName, const char *fileName)
{
   ROOT::RDataFrame d(100);
   auto i = 0.;
   d.Define("b1", [&i]() { return i; })
      .Define("b2",
              [&i]() {
                 float j = i * i;
                 ++i;
                 return j;
              })
      .Snapshot(treeName, fileName);
}

int df005_fillAnyObject()
{

   // We prepare an input tree to run on
   auto fileName = "df005_fillAnyObject.root";
   auto treeName = "myTree";
   fill_tree(treeName, fileName);

   // We read the tree from the file and create a RDataFrame.
   ROOT::RDataFrame d(treeName, fileName);

   // ## Filling any object
   // We now fill some objects which are instances of classes which expose a
   // `Fill` method with some input arguments.
   auto th1d = d.Fill<double>(TH1D("th1d", "th1d", 64, 0, 128), {"b1"});
   auto th1i = d.Fill<float>(TH1I("th1i", "th1i", 64, 0, 128), {"b2"});
   auto th2d = d.Fill<double, float>(TH2D("th2d", "th2d", 64, 0, 128, 64, 0, 1024), {"b1", "b2"});

   auto c1 = new TCanvas();
   th1d->DrawClone();

   auto c2 = new TCanvas();
   th1i->DrawClone();

   auto c3 = new TCanvas();
   th2d->DrawClone("COLZ");

   return 0;
}