tree143_drawsparse.C File Reference

Detailed Description

Convert a THnSparse to a TTree using efficient iteration through the THnSparse and draw a THnSparse using TParallelCoord.

The plot will contain one line for each filled bin, with the bin's coordinates on each axis, and the bin's content on the rightmost axis.

Run as

.L $ROOTSYS/tutorials/io/tree/tree143_drawsparse.C+

 
#include "TParallelCoord.h"
#include "TParallelCoordVar.h"
#include "TROOT.h"
#include "TTree.h"
#include "TLeaf.h"
#include "THnSparse.h"
#include "TAxis.h"
#include "TCanvas.h"
#include "TRandom.h"
#include "TFile.h"
#include "TH3.h"
 
TTree* toTree(THnSparse* h)
{
   // Creates a TTree and fills it with the coordinates of all
   // filled bins. The tree will have one branch for each dimension,
   // and one for the bin content.
 
   Int_t dim = h->GetNdimensions();
   TString name(h->GetName()); name += "_tree";
   TString title(h->GetTitle()); title += " tree";
 
   TTree* tree = new TTree(name, title);
   Double_t* x = new Double_t[dim + 1];
   memset(x, 0, sizeof(Double_t) * (dim + 1));
 
   TString branchname;
   for (Int_t d = 0; d < dim; ++d) {
      if (branchname.Length())
         branchname += ":";
      TAxis* axis = h->GetAxis(d);
      branchname += axis->GetName();
      branchname += "/D";
   }
   tree->Branch("coord", x, branchname);
   tree->Branch("bincontent", &x[dim], "bincontent/D");
 
   Int_t *bins = new Int_t[dim];
   for (Long64_t i = 0; i < h->GetNbins(); ++i) {
      x[dim] = h->GetBinContent(i, bins);
      for (Int_t d = 0; d < dim; ++d) {
         x[d] = h->GetAxis(d)->GetBinCenter(bins[d]);
      }
 
      tree->Fill();
   }
 
   delete [] bins;
   //delete [] x;
   return tree;
}
 
 
void drawsparse_draw(THnSparse* h)
{
   // Draw a THnSparse using TParallelCoord, creating a temporary TTree.
 
   TTree* tree = toTree(h);
 
   TString whatToDraw;
   TIter iLeaf(tree->GetListOfLeaves());
   const TLeaf* leaf = nullptr;
   while ((leaf = (const TLeaf*)iLeaf())) {
      if (whatToDraw.Length())
         whatToDraw += ":";
      whatToDraw += leaf->GetName();
   }
   tree->Draw(whatToDraw, "", "para");
   TParallelCoord* parallelCoord = (TParallelCoord*)gPad->GetListOfPrimitives()->FindObject("ParaCoord");
 
   TIter iVar(parallelCoord->GetVarList());
   TParallelCoordVar* var = nullptr;
   for (Int_t d = 0;(var = (TParallelCoordVar*) iVar()) && d < h->GetNdimensions(); ++d) {
      TAxis* axis = h->GetAxis(d);
      var->SetHistogramBinning(axis->GetNbins());
      var->SetCurrentLimits(axis->GetXmin(), axis->GetXmax());
      var->SetTitle(axis->GetTitle());
   }
   var->SetTitle("bin content");
}
 
void tree143_drawsparse()
{
   // create a THnSparse and draw it.
 
   const Int_t ndims = 8;
   Int_t bins[ndims] = {10, 10, 5, 30, 10, 4, 18, 12};
   Double_t xmin[ndims] = {-5., -10., -1000., -3., 0.,   0., 0., 0.};
   Double_t xmax[ndims] = {10., 70., 3000.,   3.,   5.,  2., 2., 5.};
   auto hs = new THnSparseD("hs", "Sparse Histogram", ndims, bins, xmin, xmax);
 
   // fill it
   Double_t x[ndims];
   for (Long_t i = 0; i < 100000; ++i) {
      for (Int_t d = 0; d < ndims; ++d) {
         switch (d) {
            case 0:
               x[d] = gRandom->Gaus() * 2 + 3.;
               break;
            case 1:
            case 2:
            case 3:
               x[d] = (x[d - 1] * x[d - 1] - 1.5) / 1.5 + (0.5 * gRandom->Rndm());
               break;
            default:
               x[d] = sin(gRandom->Gaus()*i/1000.) + 1.;
         }
      }
      hs->Fill(x);
   }
 
   auto f = TFile::Open("drawsparse.root", "RECREATE");
 
   auto canv = new TCanvas("hDrawSparse", "Drawing a sparse hist");
   canv->Divide(2);
 
   // draw it
   canv->cd(1);
   drawsparse_draw(hs);
 
   // project it
   canv->cd(2);
   TH3D* h3proj = hs->Projection(2, 3, 6);
   h3proj->SetLineColor(kOrange);
   h3proj->SetDirectory(nullptr);
   h3proj->Draw("lego1");
 
   // save everything to a file
   canv->Write();
   hs->Write();
   h3proj->Write();
 
   delete f;
}

Author

Axel Naumann

Definition in file tree143_drawsparse.C.