Number of entries of histogram obtained from RooDataHist is always 100

Roofit and RooStats
1

Hi Rooters,

While I was working on the binned dataset observed that a histogram created from RooDataHist has total entries always equal to 100. To illustrate this point I have attached the modified code from tutorial rf201_composite.C. Here I make a binned clone of data (see line 72) and convert it to a TH1 histogram using the createHistogram method. I observe that the number of entries shown in the statistics box of TH1 is always equal to 100. I also confirmed it by printing it h1->GetEntries(). In the example, I have generated 1000 data points and filled them into 50 bins. I expect the number of entries of the histogram to be 1000. But it shows that the number of entries is 100. Can someone explain why is this so?
rf201_composite.C (4.3 KB)

2

Hi,

Thanks for the post and reproducer. Passing through a RooDataHist is not necessary. You can directly obtain your histogram, with the right number of entries, like this:

   RooDataSet *data = model.generate(x, 123);
   
   TH1 *h1 = data->createHistogram("h1", x, Binning(50,0.0,10.0));

Cheers,
D

PS
@jonas

3

Dear Danilo,

Thanks for the reply. It worked. But I am just curious to know why the same histogram made using RooDataHist does not show the correct entries. Is it some bug?

Regards
KKR