General "look up" class for histogram that opens before looping accessed while looping

[lcorcodilos]

General "look up" class for histogram that opens before looping accessed while looping

[lcorcodilos]

Becky's first shot.

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <cstring>
#include <string>
#include "TROOT.h"
#include "TSystem.h"
#include "TTree.h"
#include "TFile.h"
#include "TH1F.h"
#include "TH2F.h"
using namespace std;
class BinHistoFunc2 {
public:
  //  BinHistoFunc(){} // Constructor without arguments
    float histoFunc(std::string histtype, std::string filename, std::string histname){ //histogram function that takes two file arguments
        TFile *F = TFile::Open(filename.c_str());
        float val;
        if (histtype=="1D"){
            TH1F *hist = (TH1F *)F->Get(histname.c_str());
            int binsx = hist->GetNbinsX();
            std::cout << "hi" << std::endl;
        //  std::cout << F << std::endl;
            std::cout << binsx << std::endl;
            for(int b = 1; b < binsx; b++){
              float val = hist->GetBinContent(b);
              std::cout << "val is " << val << std::endl;
              std::cout << "bin is " << b << std::endl;
            };
        }
        else if (histtype=="2D"){
            TH2F *hist = (TH2F *)F->Get(histname.c_str());
            int binsx = hist->GetNbinsX();
            int binsy = hist->GetNbinsY();
        //  std::cout << "hi" << std::endl;
        //  std::cout << F << std::endl;
        //      std::cout << binsx << std::endl;
            for(int bx = 1; bx < binsx; bx++){
                for(int by = 1; by < binsy; by++){
                    float val = hist->GetBinContent(bx, by);
                    std::cout << "val is " << val << std::endl;
                    // std::cout << "bin is " << b << std::endl;
                };
            };
        } 
         return val;  
    }
};
BinHistoFunc2 obj;
float a = obj.histoFunc("2D", "example.root", "MtwvMtPass");

[lcorcodilos]

There are some other tricks we can do though to make it even better

Like we can ask the type of the histogram passed in the argument to see if it inherits from TH1, TH2, or TH3 to get the dimensionality (and then you don't need it as an argument)

I'll make like a to-do list.

[lcorcodilos]

• Determine type from object passed in argument. There's something called dynamic_cast which can change an objects type to a type from which it inherits but returns NULL if it won't work. So like dynamic_cast<const TH2*>(hist)
  would return NULL if hist isn't TH2I, TH2F, etc because those all inherit from the base class TH2. We have to be careful though because all histograms in ROOT (no matter the dimension) inherit from TH1 so any if statement should check first if the histogram can be cast to TH3 or TH2 and then do TH1s as the else at the end.
• Setup the constructor to take the file and histogram names as input. Constructor will just load the histogram
• Setup histoFunc to return the bin contents of the loaded histogram. May be more appropriate to rename histoFunc to GetBinContent
• Have a second function to look up bin content by axis value instead of bin number

The 1st is probably the trickiest so feel free to go out of order.

An explicit example for the first might be:

if (<dynamic_cast>(const TH3*) F->Get(histname.c_str()) != NULL) {
 stuff...
} else if (<dynamic_cast>(const TH2*) F->Get(histname.c_str()) != NULL) {
 stuff...
} else {
 stuff..
}

No promises that it compiles though :-)

[rek81]

Version with dynamic cast
BinHistoFunc_New.txt

[lcorcodilos]

This looks great! The only thing is that I don't think I was clear about was the desired output from the functions. What you've written is actually doing more than what's needed. We just need to return a specific requested bin value (by bin number or axis value) and we don't need to loop over all bins. I'll try to explain by example. This is the beginning of your GetBinContents() function (dropping the std::cout)

float GetBinContents(void){ 
    float val;
    if (hist1 != 0) {
      int binsx = hist1->GetNbinsX();
      for(int b = 1; b < binsx; b++){
        val = hist1->GetBinContent(b);
      }
    }
    ...
   return val;

This can be simplified to this (note I also changed the function arguments):

float GetBinContents(int xbin, int ybin = 0, int zbin = 0){ 
    float val;
    if (hist1 != 0) {
      val = hist1->GetBinContent(xbin);
    }
   ...
   return val;

Let me know if that makes sense and feel free to send questions, obviously. But next step is to have GetBinContents and and GetBinContentsByAxis to just be the specific bin lookup. Then I think we can drop it in to the repo!

[lcorcodilos]

Added in PR #19