Re: smart code-help needed

Hi Chris,

On Wed, 2007-05-02 at 07:08 +0530, suneel_at_puhep.res.in wrote:
> Dear rooters,
> I want to be a smart coder but now have a very limited knowledge of
> c++ and coding techniques that is why running for help.
> I an interested in plotting few similar two dimensional histograms for a
> very large number of variables .All the histograms are going to have same
> thing along one of the axis(let us take x-axis(pt))Idea is to define the
> other axis as a variable(y) as then I can make a common fill loop.(like
> Fill(pt,y).Then I am left with only specifying value for y and get all
> the histograms.This thing will also need to define one other variable
> which could represent the histograms for different y-variables.
> To provide more clarity of what I am doing I am enclosing following three
> steps.
> 1.Defining histograms
> 2.define the loop which tells for a particular value of y fill which set
> of histograms.
> 3.Common fill.
> I am finding myself clueless in answering "how to code it".
> If some-one could provide me some help or hints regarding this then it
> could be a great help.

I'm not sure exactly what you mean by `... particular value of y fill which set of histograms ...', but I'm going to assume the worst case, which is where you have different quantities you want to put on the Y-axis (say eta, rapidity, m^2, etc):

        struct MyHists 
        {
          typedef std::multimap<int,TH2*> Map_t;
      typedef Map_t::value_type Elem_t;
          Map_t fMap;
          int fNPt;
          int fMinPt;
          int fMaxPt;
        
          MyHists(int npt, double minpt, double maxpt) 
           : fNPt(npt), fMinPt(minpt), fMaxPt(maxPt) {}
          virtual ~MyHists() {
            for (Map_t::iterator i = fMap.begin(); i != fMap.end(); ++i) 
              delete i->second;
          }
          TH2* AddHistogram(int type, int nbins, double min, double max) 
          {
         std::string n(Form("hist_%d_%d", type, fMap.count(type))); 
             TH2* r = new TH2D(n.c_str(), n.c_str(),
        	               fNPt, fMinPt, fMaxPt, nbins, min, max);
             fMap.insert(Elem_t(type, r));
             return r;
          }
          bool Fill(int type, double pt, double v) 
          {
            for (Map_t::iterator i = fMap.begin(); i != fMap.end(); ++i)
        {
              if (i->first != type) continue;
              i->second->Fill(pt, v);
        }
      }
     };
          
         void test()
     {
        enum { 
	  kRapidity, 
	  kEta
        };
	TFile f("foo.root", "RECREATE");
	MyHists h(100, 0, 100);
	h->Add(kRapidity, 10, -3, -1);
	h->Add(kRapidity, 10, -1, 0);
	h->Add(kRapidity, 10,  0, 5);
	h->Add(kEta, 10, -3, -1);
	h->Add(kEta, 10, -1, 0);
	h->Add(kEta, 10,  0, 5);
	
	for (size_t i = 0; i < 10000; i++) { 
	   int t     = (gRandom->Uniform() > .5 ? kEta : kRapidity);
	   double pt = (gRandom->Exp(30));
	   double v  = gRandom->Gaus(0, 3);
	   h->Fill(t, pt, v);
        }
	f.Write();
	f.Close();
      }

Hope that helped.

Yours,

-- 
 ___  |  Christian Holm Christensen 
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