Problem of weights while using RooDataSet->append()

[sakar]

Hello,

I’m using RooFit in ROOT 5.28.
I’m trying to built one unique dataset from two similar ones. The two initial datasets are generated from RooGaussian and then I apply two different weights to each of those datasets (i.e. 1.0 and 0.5).
Then I create an empty dataset. I fill this one with the two initial ones using the append method. However, and here is my problem, the weights seems to disappear during this operation:
(here is the code that I’m using)

...
  RooRealVar x("x","x",-10,10);

  RooRealVar m1("m1","m1",3,2,4);
  RooRealVar s1("s1","s1",2,0.5,3);
  RooGaussian gauss1("gauss1","gauss1",x,m1,s1);
  RooDataSet *d1 = gauss1.generate(x,10000);

  RooRealVar m2("m2","m2",-2,2,4);
  RooRealVar s2("s2","s2",2,0.5,3);
  RooGaussian gauss2("gauss2","gauss2",x,m2,s2);
  RooDataSet *d2 = gauss2.generate(x,10000);

  RooFormulaVar wFunc("w","event weight","(0.5)",x) ;
  RooRealVar* w = (RooRealVar*) d2->addColumn(wFunc) ;
  RooDataSet *d3_a = new RooDataSet(d2->GetName(),d2->GetTitle(),d2,*d2->get(),0,w->GetName()) ;

  RooFormulaVar wFunc("w","event weight","(1)",x) ;
  RooRealVar* w = (RooRealVar*) d1->addColumn(wFunc) ;
  RooDataSet *d3_b = new RooDataSet(d1->GetName(),d1->GetTitle(),d1,*d1->get(),0,w->GetName()) ;

  RooDataSet *d5 = new RooDataSet("d5","d5",x);
  d5->append(*d3_a);
  d5->append(*d3_b);

  d3_a->Print("v");
  d3_b->Print("v");
  d5->Print("v");
...

The PrintOut gives me:

DataStore gauss2Data (Generated From gauss2)
  Contains 10000 entries
  Observables: 
    1)  x = -3.24245  L(-10 - 10)  "x"
  Dataset variable "w" is interpreted as the event weight

DataStore gauss1Data (Generated From gauss1)
  Contains 10000 entries
  Observables: 
    1)  x = 3.37908  L(-10 - 10)  "x"
  Dataset variable "w" is interpreted as the event weight

DataStore d5 (d5)
  Contains 20000 entries
  Observables: 
    1)  x = 3.37908  L(-10 - 10)  "x"

Moreover, when I try to plot separatly the initial weighted datasets, the weights normalization is good, it only disappears when I use dataset d5.

Does someone know what I’m not during right and what should be the proper way to use the append method while handling weighted datasets ?

Thank you,
Simon

[leih]

Hello,
I meet the same problem as yours, have you solved the problem you met before? Could you please tell me how you solve it? Thank you for your help very much.
Thank you,
Lei.

[StephanH]

I think what you are looking for might have been discussed here:

Combining multiple individually weighted RooDataSets?

Ok, it wasn’t easy, but here’s what needs to be done: All datasets (the final one and the ones you use for merging) need to have a WeightVar(scale) set. You need to change the value of scale before you create the intermediate datasets. Since the original data that you Import() from don’t have values for scale, it just retains the value that it had before the dataset was created. Then append to the global dataset. Side note: The usual syntax for getting a value is getVal(). getValV() is only …

[leih]

Thank you for your help very much, I will scan it carefully.
Cheers,
Lei.