[RF] RooDataSet columns added with addColumns method not copied correctly in reduce

[will-cern]

Affects at least 6.22/08

Minimal reproducer:

{
    RooRealVar x("x","x",1);
    RooRealVar w("w","w",1);
    RooDataSet d("d","d",w,"w");

    d.addColumns(x);

    for(int i=0;i<10;i++) {
        x = i; d.add(x,0);
    }

    // d now has 10 entries with x values increasing
    for(int i=0;i<d.numEntries();i++) std::cout << d.get(i)->getRealValue("x") << ","; std::cout << std::endl;

    // now reduce the dataset and repeat:
    auto e = d.reduce("x>5");
    for(int i=0;i<e->numEntries();i++) std::cout << e->get(i)->getRealValue("x") << ","; std::cout << std::endl;
}

This outputs:

0,1,2,3,4,5,6,7,8,9,
9,9,9,9,

where it should really output:

0,1,2,3,4,5,6,7,8,9,
6,7,8,9,

If the "x" column was included when the dataset is constructed, the reduction works correctly.

[will-cern]

incredibly, addColumn works ok though, so hopefully the problem is easy to track down by comparing those two methods.

I originally tried to workaround the problem by creating another dataset and merging it in. I discovered that suffers from another bug though that merged datasets lose their weightedness!

[github-actions]

Hi @guitargeek,

It appears this issue is closed, but wasn't yet added to a project. Please add upcoming versions that will include the fix, or 'not applicable' otherwise.

Sincerely,
🤖